Question

Use Pythagorean identity to find sin (0) if 0 is in quadrant III

Answer 1

Given that:

TanФ = 5√11/11

Using SOH CAH TOA

Sin Ф = opp/hyp

CosФ = adj/hyp

TanФ = opp/adj

Therefore,

From the given identity we can say that:

Opposite = 5√11

Adjacent = 11

Using Pythagoras formula:

a² + b² = c²

Where c is the hypotenuse, a and b are the opposite and adjacent.

We can now find the hypotenuse.

(5√11)² + 11² = c²

(25 × 11) + 121 = c²

275 + 121 = c²

396 = c²

Taking square root on both sides,

we get:

c = √396

c = 6√11

Now, we have all the three sides and again using SOH CAH TOA, we can figure out the exact value of Sin Ф.

Sin Ф = Opp/Hyp

Sin Ф =5√11 /6√11

Canceling the like terms,

we get:

Sin Ф =5/6

Now, we know that, in the third quadrant, only TanФ is positive and the rest of the trigonometric values are negative, we will have the negative value of the opposite side.

Hence,

 Sin Ф = - 5/6