Question

Which of the following quadratic equations can be solved by grouping?(1 point)
Responses

x^2−4x−8=0

x squared minus 4 x minus 8 equals 0

x^2+10x+21=0

x squared plus 10 x plus 21 equals 0

x^2+8x−22=0

x squared plus 8 x minus 22 equals 0

x^2−12x+18=0

x squared minus 12 x plus 18 equals 0

Answer 1

x^2 + 10x + 21 = 0

Because 21 = 3·7 and 3 + 7 = 10, you can split 10x as 3x + 7x and factor by grouping:
x^2 + 3x + 7x + 21 = x(x + 3) + 7(x + 3) = (x + 3)(x + 7).