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2a\left(a+1\right)+\left(a+1\right)\left(-1\right)=a+7
Variable a cannot be equal to -1 since division by zero is not defined. Multiply both sides of the equation by a+1.
2a^{2}+2a+\left(a+1\right)\left(-1\right)=a+7
Use the distributive property to multiply 2a by a+1.
2a^{2}+2a-a-1=a+7
Use the distributive property to multiply a+1 by -1.
2a^{2}+a-1=a+7
Combine 2a and -a to get a.
2a^{2}+a-1-a=7
Subtract a from both sides.
2a^{2}-1=7
Combine a and -a to get 0.
2a^{2}=7+1
Add 1 to both sides.
2a^{2}=8
Add 7 and 1 to get 8.
a^{2}=\frac{8}{2}
Divide both sides by 2.
a^{2}=4
Divide 8 by 2 to get 4.
a=2 a=-2
Take the square root of both sides of the equation.
2a\left(a+1\right)+\left(a+1\right)\left(-1\right)=a+7
Variable a cannot be equal to -1 since division by zero is not defined. Multiply both sides of the equation by a+1.
2a^{2}+2a+\left(a+1\right)\left(-1\right)=a+7
Use the distributive property to multiply 2a by a+1.
2a^{2}+2a-a-1=a+7
Use the distributive property to multiply a+1 by -1.
2a^{2}+a-1=a+7
Combine 2a and -a to get a.
2a^{2}+a-1-a=7
Subtract a from both sides.
2a^{2}-1=7
Combine a and -a to get 0.
2a^{2}-1-7=0
Subtract 7 from both sides.
2a^{2}-8=0
Subtract 7 from -1 to get -8.
a=\frac{0±\sqrt{0^{2}-4\times 2\left(-8\right)}}{2\times 2}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 2 for a, 0 for b, and -8 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
a=\frac{0±\sqrt{-4\times 2\left(-8\right)}}{2\times 2}
Square 0.
a=\frac{0±\sqrt{-8\left(-8\right)}}{2\times 2}
Multiply -4 times 2.
a=\frac{0±\sqrt{64}}{2\times 2}
Multiply -8 times -8.
a=\frac{0±8}{2\times 2}
Take the square root of 64.
a=\frac{0±8}{4}
Multiply 2 times 2.
a=2
Now solve the equation a=\frac{0±8}{4} when ± is plus. Divide 8 by 4.
a=-2
Now solve the equation a=\frac{0±8}{4} when ± is minus. Divide -8 by 4.
a=2 a=-2
The equation is now solved.