Solve {l}{5500=946lambda+b}{2750=948lambda+b}

$$\left\{ \begin{array} { l } { 5500 = 946 \lambda + b } \\ { 2750 = 948 \lambda + b } \end{array} \right.$$

Solve for λ, b

$$\lambda =-1375$$

$$b=1306250$$

Steps Using Substitution

Consider the first equation. Swap sides so that all variable terms are on the left hand side.

$$946\lambda +b=5500$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$948\lambda +b=2750$$

To solve a pair of equations using substitution, first solve one of the equations for one of the variables. Then substitute the result for that variable in the other equation.

$$946\lambda +b=5500,948\lambda +b=2750$$

Choose one of the equations and solve it for \lambda by isolating \lambda on the left hand side of the equal sign.

$$946\lambda +b=5500$$

Subtract b from both sides of the equation.

$$946\lambda =-b+5500$$

Divide both sides by 946.

$$\lambda =\frac{1}{946}\left(-b+5500\right)$$

Multiply \frac{1}{946} times -b+5500.

$$\lambda =-\frac{1}{946}b+\frac{250}{43}$$

Substitute -\frac{b}{946}+\frac{250}{43} for \lambda in the other equation, 948\lambda +b=2750.

$$948\left(-\frac{1}{946}b+\frac{250}{43}\right)+b=2750$$

Multiply 948 times -\frac{b}{946}+\frac{250}{43}.

$$-\frac{474}{473}b+\frac{237000}{43}+b=2750$$

Add -\frac{474b}{473} to b.

$$-\frac{1}{473}b+\frac{237000}{43}=2750$$

Subtract \frac{237000}{43} from both sides of the equation.

$$-\frac{1}{473}b=-\frac{118750}{43}$$

Multiply both sides by -473.

$$b=1306250$$

Substitute 1306250 for b in \lambda =-\frac{1}{946}b+\frac{250}{43}. Because the resulting equation contains only one variable, you can solve for \lambda directly.

$$\lambda =-\frac{1}{946}\times 1306250+\frac{250}{43}$$

Multiply -\frac{1}{946} times 1306250.

$$\lambda =\frac{-59375+250}{43}$$

Add \frac{250}{43} to -\frac{59375}{43} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$\lambda =-1375$$

The system is now solved.

$$\lambda =-1375,b=1306250$$

Steps Using Matrices

Consider the first equation. Swap sides so that all variable terms are on the left hand side.

$$946\lambda +b=5500$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$948\lambda +b=2750$$

Put the equations in standard form and then use matrices to solve the system of equations.

$$946\lambda +b=5500,948\lambda +b=2750$$

Write the equations in matrix form.

$$\left(\begin{matrix}946&1\\948&1\end{matrix}\right)\left(\begin{matrix}\lambda \\b\end{matrix}\right)=\left(\begin{matrix}5500\\2750\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}946&1\\948&1\end{matrix}\right).

$$inverse(\left(\begin{matrix}946&1\\948&1\end{matrix}\right))\left(\begin{matrix}946&1\\948&1\end{matrix}\right)\left(\begin{matrix}\lambda \\b\end{matrix}\right)=inverse(\left(\begin{matrix}946&1\\948&1\end{matrix}\right))\left(\begin{matrix}5500\\2750\end{matrix}\right)$$

The product of a matrix and its inverse is the identity matrix.

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}\lambda \\b\end{matrix}\right)=inverse(\left(\begin{matrix}946&1\\948&1\end{matrix}\right))\left(\begin{matrix}5500\\2750\end{matrix}\right)$$

Multiply the matrices on the left hand side of the equal sign.

$$\left(\begin{matrix}\lambda \\b\end{matrix}\right)=inverse(\left(\begin{matrix}946&1\\948&1\end{matrix}\right))\left(\begin{matrix}5500\\2750\end{matrix}\right)$$

For the 2\times 2 matrix \left(\begin{matrix}a&b\\c&d\end{matrix}\right), the inverse matrix is \left(\begin{matrix}\frac{d}{ad-bc}&\frac{-b}{ad-bc}\\\frac{-c}{ad-bc}&\frac{a}{ad-bc}\end{matrix}\right), so the matrix equation can be rewritten as a matrix multiplication problem.

$$\left(\begin{matrix}\lambda \\b\end{matrix}\right)=\left(\begin{matrix}\frac{1}{946-948}&-\frac{1}{946-948}\\-\frac{948}{946-948}&\frac{946}{946-948}\end{matrix}\right)\left(\begin{matrix}5500\\2750\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}\lambda \\b\end{matrix}\right)=\left(\begin{matrix}-\frac{1}{2}&\frac{1}{2}\\474&-473\end{matrix}\right)\left(\begin{matrix}5500\\2750\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}\lambda \\b\end{matrix}\right)=\left(\begin{matrix}-\frac{1}{2}\times 5500+\frac{1}{2}\times 2750\\474\times 5500-473\times 2750\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}\lambda \\b\end{matrix}\right)=\left(\begin{matrix}-1375\\1306250\end{matrix}\right)$$

Extract the matrix elements \lambda and b.

$$\lambda =-1375,b=1306250$$

Steps Using Elimination

Consider the first equation. Swap sides so that all variable terms are on the left hand side.

$$946\lambda +b=5500$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$948\lambda +b=2750$$

In order to solve by elimination, coefficients of one of the variables must be the same in both equations so that the variable will cancel out when one equation is subtracted from the other.

$$946\lambda +b=5500,948\lambda +b=2750$$

Subtract 948\lambda +b=2750 from 946\lambda +b=5500 by subtracting like terms on each side of the equal sign.

$$946\lambda -948\lambda +b-b=5500-2750$$

Add b to -b. Terms b and -b cancel out, leaving an equation with only one variable that can be solved.

$$946\lambda -948\lambda =5500-2750$$

Add 946\lambda to -948\lambda .

$$-2\lambda =5500-2750$$

Add 5500 to -2750.

$$-2\lambda =2750$$

Divide both sides by -2.

$$\lambda =-1375$$

Substitute -1375 for \lambda in 948\lambda +b=2750. Because the resulting equation contains only one variable, you can solve for b directly.

$$948\left(-1375\right)+b=2750$$

Multiply 948 times -1375.

$$-1303500+b=2750$$

Add 1303500 to both sides of the equation.

$$b=1306250$$

The system is now solved.

$$\lambda =-1375,b=1306250$$