Question

What is the value of 'c' so that -9 and 9 are both solutions of x^2+c=103?

Answer 1

c = 22

Explanation:

x^2 + c = 103 so if x is either + or - 9, x^2 = 81 so...

81 + c = 103

c = 22

Answer 2

c = 22

Explanation:

Remark

You have to make c large enough so that when subtracted from 103, you get 81

Solution

x^2 + c = 103

x = 9

9^2 + c = 103

81 + c = 103

Subtract 81 from both sides

81 - 81 + c = 103 - 81

c = 22

- 9 does exactly the same thing.

Check

x^2 + 22 = 103

x^2 - 22 = 103 - 22

x^2 = 81

sqrt(x^2) = sqrt(81)

x = +/- 9