y=4x-9 y=x-3

Question

I don't understand substitution

y=4x-9

y=x-3

Answer 1

Answer: it means to substitute the first equation of y into the second equation of y; substitution means "replacement".

4x - 9 = x - 3,  4x - x = 9 - 3, 3x = 6, hence, x = 2;

 

x = 2 satisfies both y = 4 * (2) - 9 = -1, and y = 2 - 3 = -1.