If cosa = 3/5 and a ∈ (630,720), find sin2a

-

Step-by-step explanation:

Given 630 < A > 720 then A is in the fourth quadrant where

cosA > 0 and sinA < 0

Given

cosA = =

Then the triangle is a 3- 4 - 5 with opposite side 4, thus

sinA = - = -

Using the trigonometric identity

sin2A = 2sinAcosA

         = 2 × - ×

         = = -

the direct variation says that:

then the equation is of the form is given by:

            where k is the constant variation.

from the given table:

consider any value of x and m(x)=y

x = 2 and m(x)=y = 3

substitute these value in [1]; we have;

divide both sides by 2 we get;

⇒

check:

put x = -1 and m(x) = -1.5

substitute in the equation:

-1.5 = -1.5                   true

therefore, the function m(x) represents a direct variation

graph of this function as shown below: