2x^2+7x-9=0 3x^2=18x 100x^2-16=0 x^2-16x+63=0

1)  2x^2+7x-9=0

x1= (-7-√(49+72))/4 = -18/4= - 9/2
x2= (-7+√(49+72))/4 = 1

2)  3x^2=18x

3x(x-6)=0  
x1=0  x2=6

3)  100x^2-16=0
4(5x-2)(5x+2)=0
x1=2/5   x2=-2/5

4)  x^2-16x+63=0

x1=(16-√(16²-4·63))/2=(16-2)/2=7   x2=(16+√(16²-4·63))/2=(16+2)/2=9