4a^2+8a-20=0

By completing the square

4a² + 8a - 20 = 0

a = - 8 + / - √ (8² - 4 (4) (-20))

2 (4)

a = - 8 + / - √ (64 + 320)

8

a = - 8 + / - √384

8

a = - 8 + / - 19.59591794

8

a = - 8 + 19.59591794 a = - 8 - 19.59591794

8 8

a = 11.59591794 a = - 27.59591794

8 8

a = 1.449489743 a = - 3.443813782

I'm not sure but I think it is a=-1± 6√

a≈1.44948974, - 3.44948974