Homework Help: Math

Posted by David on Monday, June 14, 2010 at 2:44pm.

I need help with these problems for a test.
1. Find the inverse of the one-to-one function.
f(x)=5x+1/4.

2. The height of the water, H, in feet, at a boat dock t hours after 7 am is given by E=7+4.4cos pi/35 t, where t is time measured in seconds. Find the period.

3. Solve the equation on the interval [0, 2pi).
a) sin^2x - cos^2x = 0

b) sin4x=(sq3)/2

4. Factor completely, or state that the polynomial is prime.
27y^4-147y^2

Math - Reiny, Monday, June 14, 2010 at 5:14pm
1. Here is a neat way to find the inverse of a linear function.
perform the inverse of the operations in reverse order

original: we multiply by 5 then add 1/4
inverse: we subtract 1/4, then divide by 5
f^-1(x) = (x - 1/4)/5
= (4x-1)/20

check: pick any value of x, e.g. x = 8
f(8) = 40+1/4 = 161/4

f^-1(161/4) = (4(161/4) - 1))/20
= 160/20 = 8
checks out!
Math - Reiny, Monday, June 14, 2010 at 5:17pm
2. The period of E = 7+4.4cos(π/35)t
= 2π/(π/35)
= 70
Math - Reiny, Monday, June 14, 2010 at 5:27pm
3. sin^2x - cos^2x = 0
sin^2x - (1 - sin^2x) = 0
2sin^2x = 1
sin^2x = 1/2
sin x = ą 1/√2

x = 45°, 135°, 225° or 315°
or
x = π/4, 3π/4, 5π/4 or 7π/4

4. sin 4x = √3/2
4x = 60° or 4x = 120°
or
4x = π/3 or 4x = 2π/3

so x = π/12 or x = 2π/12 = π/6

but the period of sin4x is 90° or π/2
so by adding π/2 to each of the above answers we can get more answers until we go past 2π

π/12 + π/2 = 7π/12
7π/12 + π/2 = 13π/12
13π/12 + π/2 = 19π/12 adding one more π/2 would be beyond 2π

now do the same with π/6 to get 3 more answers from that branch

altogether there will be 8 different solutions.
Math - Reiny, Monday, June 14, 2010 at 5:28pm
lastly, .....

27y^4-147y^2
= 3y^2(9y^2 - 49)
= 3y^2(3y+7)(3y-7)
Math - David, Monday, June 14, 2010 at 7:48pm
Thanks

Answer this Question

Related Questions

Algebra-One to one function - Could you please check my answers and help me with...
Math - I need help with these problems for a test. 1. Find the inverse of the ...
Algebra Help Inverse One-to-one - Did I do this right? Problem: If the ...
Alegbra - I need to have some problems checked and I need help with one of them...
math! - about finding the inverse of y=(2x+1)/(x+3). should you multiply (x+3) ...
PreCalc! - sketch a graph whose domain is the interval [0, infinity) but whose ...
pre-calculus - the function f(x)=4/x-7 is one to one a. find the inverse of f b...
Math - determine if the given function is one-to-one. if it is, find the inverse...
MATH PLEASE HELP - Given: Let f: X -> Y be a function. Then we have an ...
inverse - If f(x)=cosx + 3 how do I find f inverse(1)? Thanks y = cos(x) + 3 the...

For Further Reading

First Name:
School Subject:
Answer: