Let 0° < a < 90°
Given: cos a=7/25
Find: sin a and cot a

The solutions are:

sin(a)  = 24/25

tan(a) = 24/7

For a given point (x, y) and an angle "a" measured counterclockwise from the positive x-axis to a ray that connects the origin with our point, we can think on the situation as a triangle rectangle.

Where the ray is the hypotenuse, the x-component is the adjacent cathetus, and the y-component is the opposite cathetus.

So we have:

x = adjacent cathetus

y = opposite cathetus

h = hypotenuse = √(x^2 + y^2)

Then the trigonometric relations become:

cos(a) = x/√(x^2 + y^2)

sin(a) = y/√(x^2 + y^2)

tan(a) = y/x

Now, we know that we have:

cos(a) = 7/25

then we can see that:

x = 7

and

h = 25 = √(7^2 + y^2)

We can solve the above equation for y:

25 = √(7^2 + y^2)

25 = √(49 + y^2)

25^2 = 49 + y^2

625 - 49 = y^2

√576 = y = 24

Then we have:

x = 7

y = 24

h = 25

Now we can return to our known trigonometric relations and get:

sin(a) = y/√(x^2 + y^2) = 24/25

tan(a) = y/x = 24/7

If you want to learn more about trigonometry, you can read: