a)By completing the square, prove the quadratic formula starting from ax^2+bx+c=0, b) hence, or otherwise solve 3x^2 + 7x -2= 9, to 3s.f.

a)starting from ax²+bx+c=0, divide through by a, x²+(b/a)x+c/a=0, complete the square (x+(b/2a))²-(b/2a)² +c/a=0, expand (x+(b/2a))²-(b²/4a²)+c/a=0, Combine fractions and rearrange,(x+(b/2a))²=(b²-4ac)/4a², square root both sides, x+b/2a=±√(b²-4ac)/2a, minus b/2a from both sides and obtain quadratic formula of x=(-b±√(b²-4ac))/2a.
b)3x² + 7x -2= 9, to use quadratic formula, equation must equal 0, 3x² + 7x -11=0 , x=(-7±√(7²-43-11))/2*3 =1.08 or -3.41 (3s.f.)