7x-12=x^2

7x-12-x^2=0

-x^2-7x+12=0

x=-(-7)+-корень (-7)^2-4*1*12/2*1

x=7+-корень 49-48/2

x=7+-корень1/2

x=7+-1/2

x=7+1/2

x=7-1/2

x=4

x=3