What equations do i uue for this?

Question

Answer 1

y= x^2+7x

3x-y=-21

graph the two equations and find where they intersect

= about (3,30) and (-7,0)

It's a straight line intersecting a parabola in two points

3x -x^2 -7x = -21

x^2 +4x -21 = 0

factor, complete the square or use the quadratic formula

=(x-3)(x+7)=0

x=3, -7

y=9+21, 49-49 = 30,0

x = -4/2 + or - (1/2)sqr(16 +84))

= (-4 +/- sqr100)/2= 3, -7

y = 30,0

Answer 2

NOTE that the quadratic formula can be used to solve for x after the value for y has been substituted into the othe equation.

Answer 3

Use substitution

y = x² + 7x

3x - y = -21

3x - ( x² + 7x) = -21

Can you solve for x and answer?