Solve for x
x=\frac{21-y}{4}
Solve for y
y=21-4x
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y=-4x+21
Add 16 and 5 to get 21.
-4x+21=y
Swap sides so that all variable terms are on the left hand side.
-4x=y-21
Subtract 21 from both sides.
\frac{-4x}{-4}=\frac{y-21}{-4}
Divide both sides by -4.
x=\frac{y-21}{-4}
Dividing by -4 undoes the multiplication by -4.
x=\frac{21-y}{4}
Divide y-21 by -4.
y=-4x+21
Add 16 and 5 to get 21.
Examples
Quadratic equation
{ x } ^ { 2 } - 4 x - 5 = 0
Trigonometry
4 \sin \theta \cos \theta = 2 \sin \theta
Linear equation
y = 3x + 4
Arithmetic
699 * 533
Matrix
\left[ \begin{array} { l l } { 2 } & { 3 } \\ { 5 } & { 4 } \end{array} \right] \left[ \begin{array} { l l l } { 2 } & { 0 } & { 3 } \\ { -1 } & { 1 } & { 5 } \end{array} \right]
Simultaneous equation
\left. \begin{cases} { 8x+2y = 46 } \\ { 7x+3y = 47 } \end{cases} \right.
Differentiation
\frac { d } { d x } \frac { ( 3 x ^ { 2 } - 2 ) } { ( x - 5 ) }
Integration
\int _ { 0 } ^ { 1 } x e ^ { - x ^ { 2 } } d x
Limits
\lim _{x \rightarrow-3} \frac{x^{2}-9}{x^{2}+2 x-3}