2r - 4 2(r - 2)
--------- = ----------- = 2
r - 2 r - 2
answer
2
As it has a maximum value the coefficient of x^2 will be negative
The vertex will be at (-8,2) so in vertex form it is
y = a(x + 8)^2 + 2
and as it passes through (-7,-1) we have:
-1 = a(-7+8)^2 + 2
-1 = a + 2 so a = -3
answer is y = -3(x + 8)^2 + 2
in standard form this is y = -3x^2 -48x - 190
We have two points so we can find the gradient using y1-y2/x1-x2
gradient = 21-27/2-8
= 1
we know the form for any linear equation is y = mx + c
we have m and a point so we can substitute in point (2,21) to find c
21 = 1 x 2 + c
c = 19
therefore, the equation is y = x + 19
Remark
One of the things you need to do is learn to read phrase by phrase.
What is the quotient of a number and 7? That meas you have a number, x, and it is divided by 7. What you do that the answer you get is the quotient.
x/7 is what you know so for. Now the first part says you take 12 away from that.
x/7 - 12 is what you have after doing that.
The result you get is - 2
x/7 - 12 = - 2 Add 12 to both sides
x/7 - 12 + 12 = - 2 + 12
x/7 = 10 Now multiply by 7
x = 10 *7
x = 70 <<< Answer the number is 70
