Area of triangle

Part a answer=120cm^2
With part b in the question which is on the attachment, why can't you do
A=1/2 absinC
120=(17)(17)sinC=120
C=0.98 radians

So angle COD= 0.98 radians
Why is this wrong? The correct answer=2.16 radians

Thank you.

Because 1/2 ab SinC works in degrees

Because 1/2 ab SinC works in degrees

Can you please help me with part c:
Calculate, giving answers to 2 decimal places:
The area of the shaded region R.

Here's my working out:
Area of shaded region R=total area of larger sector with arc A₁ - area of smaller sector with arc A₂

Area of shaded region R=CA₁D total area - CA₂D area
$=\frac{1}{2}(15)^2 (\pi) - \frac{1}{2}(17)^2 (\pi)[br]=-32\pi$

This wrong, but why? How do you do this question.

Part a answer=120cm^2
With part b in the question which is on the attachment, why can't you do
A=1/2 absinC
120=(17)(17)sinC=120
C=0.98 radians

So angle COD= 0.98 radians
Why is this wrong? The correct answer=2.16 radians

Thank you.

The equation 1/2 ab sin C for the area of a triangle works just as well in radians as it does in degrees.

The equation 1/2 ab sin C for the area of a triangle works just as well in radians as it does in degrees. The problem you have is that, having correctly established that the sine of the angle you are interested in is 240/289, you have trusted your calculator to tell you what the angle is. And it has told you one possible value - but it is not the value you want! Can you see why not, and which of the other values (out of an infinite number of possibilities) is the one that you really want?