✔ 最佳答案
x^2 + (x+7)^2 = (2x+1)^2
First expand the brackets. The expansion of the binomial (a+b)^2 = a^2 + 2ab + b^2.
x^2 + (x^2 + 14x + 49) = (4x^2 + 4x + 1)
2x^2 + 14x + 49 = 4x^2 + 4x + 1
Move all terms to the left side. Remember to switch signs as you switch sides.
2x^2 - 4x^2 + 14x - 4x + 49 - 1 = 0
-2x^2 + 10x + 48 = 0
Divide every term by -2. This will make later steps a little easier.
x^2 - 5x - 24 = 0
Think of two numbers that multiply to -24 (thus their signs are opposite) and add to -5. This tells me that the two numbers, ignoring their signs, have a difference of 5 and the larger value is negative. This works for 3 and -8.
(x+3)(x-8) = 0
A product of 0 only happens when one of its factors is 0. Therefore,
x + 3 = 0 OR x - 8 = 0
x = -3 or x = 8