Homework Help: Algebra

Posted by Eric on Friday, March 22, 2013 at 5:02pm.

Please help I can't figure out these two.

Express f(x) in the form a(x − h)2 + k.
f(x) = −4x2 + 24x − 9

Find the standard equation of a parabola that has a vertical axis and satisfies the given conditions.

vertex (0, −7), passing through (3, 38)

Thank You!

Algebra - Reiny, Friday, March 22, 2013 at 5:11pm
for the first, complete the square:

f(x) = -4(x^2 - 6x ......) - 9
= -4( x^2 - 6x + 9 -9) - 9
= -4( (x-3)^2 - 9) - 9
= -4(x-3)^2 + 36 - 9
= -4(x-3)^2 + 27

for the second, you know the vertex is (0,-7)
so f(x) = a(x-0)^2 - 7
= ax^2 - 7
but (3,38) lies on it, so
38 = a(9)
a = 38/9

f(x) = (38/9)x^2 -7
Algebra - Steve, Friday, March 22, 2013 at 5:11pm
f(x) = -4(x^2-6x) - 9
= -4(x^2-6x+9) -4(-9) - 9
= -4(x-3)^2 + 27

f(x) = a(x-0)^2 - 7
38 = 9a-7
a = 5
f(x) = 5x^2 - 7
go with Steve's end # Algebra - Reiny, Friday, March 22, 2013 at 5:13pm
don't know where my - 7 went ????
Algebra - Eric, Friday, March 22, 2013 at 5:20pm
Thank You Guys!!!

Answer this Question

Related Questions

biology - Given the part of the molecule shown below, can the underlined atom ...
algebra - Which of the following is equivalent to the expression (t2 &#8722...
vector - For any two numbers a and b, the product of a−b times itself ...
Math - First, give the technology formula for the given function and then use ...
chemistry - For which of these elements would the electron affinity process ...
chemistry - For which of these elements would the electron affinity process ...
Calculus Please Help - Find a formula for a curve of the form y=e^((−(...
math - For the next three problems, evaluate each expression if x = −2...
Calculus (urgent!!) - Find a formula for a curve of the form y=e^((−(x...
Calculus (urgent!!) - Find a formula for a curve of the form y=e^((−(x...

For Further Reading

First Name:
School Subject:
Answer: