solve using the square root property: (x+7)^2=81?

2008-02-14 1:22 pm

回答 (8)

2008-02-14 1:26 pm
✔ 最佳答案
(x+7)^2 = 81 = 9^2
Taking sqrt of both sides

(x+7) = +/- 9

or x+7 = 9 and x+7 = -9

x+7=9 gives x = 2 and x+7 = -9 gives x = -16

So both the values of x i.e. 2 and -16 satisfy the given equation.
參考: primrosh
2008-02-14 1:25 pm
(x+7)² = 81
x + 7 = ± 9

for x + 7 = 9
x =2

for x + 7 = - 9
x = - 16
2008-02-14 1:29 pm
(x + 7)^2 = 81. Square root both sides.
x + 7 = 9. x + 7 = -9.
x = 2. x = -16.

Hope this helps.
2016-12-05 9:35 pm
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2008-02-14 1:32 pm
x^2+14x+49=81
x^2+14x-32=0

14^2-4(-32)=
196+128=
324

x1=-16
x2=2
2008-02-14 1:29 pm
(x + 7)^2 = 81
(x + 7)(x + 7) = 81
x^2 + 7x + 7x + 49 = 81
x^2 + 14x = 81 - 49
x^2 + 14x = 32
x^2 + 14x - 32 = 0
(x + 16)(x - 2) = 0

x + 16 = 0
x = -16

x - 2 = 0
x = 2
2008-02-14 1:28 pm
Take the square root on both sides.

If you write both sides as multiplication:

(x+7)*(x+7) = 9*9

taking the square root of a square is easy.

√(a*a) = a

However, remember that a square root can be positive or negative.

If the original number is a^2, then it could be factored as (-a)*(-a); so that -a is also a square root of a^2

You'll get
(x+7) = +/- 9

You'll need to solve using +9 (one answer) and then again, using -9 (another answer)
2008-02-14 1:27 pm
(x + 7)^2 = (x + 7) (x + 7)

x^2 + 14x + 49 = 81
x^2 + 14x - 32 = 0
(x + 16) (x - 2) = 0
x = -16 or 2


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