Math Grade 11 Identeties and equations

 

The graphs of f(θ) = 2sin(θ) - 1 (blue) , and g(θ) = 3cos(θ) + 2 (red) are shown above.


What equation would have the intersection points of the graphs as its solutions?

 

Expert Answers

An illustration of the letter 'A' in a speech bubbles

You need to find the points of intersection between the graphs of `f(theta)`  and `g(theta), ` hence, should solve the following equation such that:

`f(theta) = g(theta) => 2 sin theta - 1 = 3 cos theta + 2`

`2 sin theta - 3 costheta = 3`

You should use the following trigonometric identities such that:

`sin theta = (2tan(theta/2))/(1 + tan^2(theta/2))`

`cos theta = (1 - tan^(theta/2))/(1 + tan^2(theta/2))`

Substituting t for `tan(theta/2) ` yields:

`2*(2t)/(1 + t^2) - 3*(1 - t^2)/(1 + t^2) = 3`

You need to bring the terms to a common denominator such that:

`4t - 3 + 3t^2 - 3 - 3t^2 = 0`

Reducing like terms yields:

`4t - 6 = 0 => t = 6/4 => t = 3/2`

You need to solve for x the equation `tan(theta/2) = 3/2 => theta = 2arctan(3/2) + npi` .

Hence, the equation that has as solutions the points of intersection of graphs is `2 sin theta - 3 cos theta - 3 = 0`  and the general solution to this equation is `theta = 2arctan(3/2) + npi.`

See eNotes Ad-Free

Start your 48-hour free trial to get access to more than 30,000 additional guides and more than 350,000 Homework Help questions answered by our experts.

Get 48 Hours Free Access
Approved by eNotes Editorial