solve these simultaneous equations?

Question

y=2x-7
x^2+y^2=61

Answer 1

Substituting the value of y in terms of x from the first equation into the one

x^2 + (2x - 7)^2 = 61
x^2 + 4x^2 - 28x + 49 = 61
5x^2 - 28x - 12 = 0
5x^2 - 30x + 2x - 12 = 0
5x(x - 6) + 2(x - 6) = 0
(5x + 2)(x - 6) = 0

So either x = -2/5 = -0.4 or x = 6

Thus, y = 2x - 7 is either y = -7.8 or y = 5

Answer 2

x^2+y^2=61 y=2x-7
x^2+(2x-7)^2=61
x^2+(4x^2-28x+49)=61
5x^2-28x+49=61
5x^2-28x=12
x(5x-28)=12
-.4(-2-28)=12
-.4(-30)=12

x=-0.4
y=-7.8

Answer 3

x = 6 and y = 5
or x = - 0.4 and y = -7.8