Given that and , where angle and angle are in the same quadrant, find the exact values of
- (i)
- (ii)
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Worked solution
4(i)
1. Determine the quadrant for angles A and B
Since (negative) and (negative), and they are in the same quadrant, both and must be in the 3rd quadrant.
2. Find the exact values of tan A and tan B
In the 3rd quadrant, tangent is positive.
For angle : opposite = 3, hypotenuse = 5 adjacent = .
For angle : adjacent = 8, hypotenuse = 17 opposite = .
3. Apply the compound angle formula for tan(A + B)
4. Substitute the values and evaluate
4(ii)
1. Determine the quadrant of angle $B$ and $\frac{B}{2}$
Since , is in the 3rd or 4th quadrant.
Since , is in the 2nd or 3rd quadrant.
Given that and are in the same quadrant, they must both be in the 3rd quadrant.
Therefore, .
Dividing by 2 gives , which means is in the 2nd quadrant.
In the 2nd quadrant, is negative.
2. Apply the double angle formula for cosine to find $\cos^2 \frac{B}{2}$
Using the identity :
3. Solve for $\cos \frac{B}{2}$ and select the correct sign
Since must be negative:
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