Solve (v+5)(v-4)=10

$$( v + 5 ) ( v - 4 ) = 10$$

Solve for v

$$v=-6$$

$$v=5$$

Steps Using the Quadratic Formula

Use the distributive property to multiply v+5 by v-4 and combine like terms.

$$v^{2}+v-20=10$$

Subtract 10 from both sides.

$$v^{2}+v-20-10=0$$

Subtract 10 from -20 to get -30.

$$v^{2}+v-30=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, 1 for b, and -30 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$v=\frac{-1±\sqrt{1^{2}-4\left(-30\right)}}{2}$$

Square 1.

$$v=\frac{-1±\sqrt{1-4\left(-30\right)}}{2}$$

Multiply -4 times -30.

$$v=\frac{-1±\sqrt{1+120}}{2}$$

Add 1 to 120.

$$v=\frac{-1±\sqrt{121}}{2}$$

Take the square root of 121.

$$v=\frac{-1±11}{2}$$

Now solve the equation v=\frac{-1±11}{2} when ± is plus. Add -1 to 11.

$$v=\frac{10}{2}$$

Divide 10 by 2.

$$v=5$$

Now solve the equation v=\frac{-1±11}{2} when ± is minus. Subtract 11 from -1.

$$v=-\frac{12}{2}$$

Divide -12 by 2.

$$v=-6$$

The equation is now solved.

$$v=5 v=-6$$

Steps for Completing the Square

Use the distributive property to multiply v+5 by v-4 and combine like terms.

$$v^{2}+v-20=10$$

Add 20 to both sides.

$$v^{2}+v=10+20$$

Add 10 and 20 to get 30.

$$v^{2}+v=30$$

Divide 1, the coefficient of the x term, by 2 to get \frac{1}{2}. Then add the square of \frac{1}{2} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$v^{2}+v+\left(\frac{1}{2}\right)^{2}=30+\left(\frac{1}{2}\right)^{2}$$

Square \frac{1}{2} by squaring both the numerator and the denominator of the fraction.

$$v^{2}+v+\frac{1}{4}=30+\frac{1}{4}$$

Add 30 to \frac{1}{4}.

$$v^{2}+v+\frac{1}{4}=\frac{121}{4}$$

Factor v^{2}+v+\frac{1}{4}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(v+\frac{1}{2}\right)^{2}=\frac{121}{4}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(v+\frac{1}{2}\right)^{2}}=\sqrt{\frac{121}{4}}$$

Simplify.

$$v+\frac{1}{2}=\frac{11}{2} v+\frac{1}{2}=-\frac{11}{2}$$

Subtract \frac{1}{2} from both sides of the equation.

$$v=5 v=-6$$