Question

Angles α and β are angles in standard position such that: α terminates in Quadrant I and sinα = 3/5 β terminates in Quadrant III and tanβ = 5/12 . Find sin(α - β).

Answer 1

-16/65

Explanation:

Given sinα = 3/5 in quadrant 1;

Since sinα = opp/hyp

opp = 3

hyp = 5

adj^2 = hyp^2 - opp^2

adj^2 = 5^2 = 3^2

adj^2 = 25-9

adj^2 = 16

adj = 4

Since all the trig identity are positive in Quadrant 1, hence;

cosα = adj/hyp = 4/5

Similarly, if tanβ = 5/12 in Quadrant III,

According to trig identity

tan theta = opp/adj

opp = 5

adj = 12

hyp^2 = opp^2+adj^2

hyp^2 = 5^2+12^2

hyp^2 = 25+144

hyp^2 = 169

hyp = 13

Since only tan is positive in Quadrant III, then;

sinβ = -5/13

cosβ = -12/13

Get the required expression;

sin(α - β) = sinαcosβ - cosαsinβ

Substitute the given values

sin(α - β) = 3/5(-12/13) - 4/5(-5/13)

sin(α - β)= -36/65 + 20/65

sin(α - β) = -16/65

Hence the value of sin(α - β) is -16/65