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11. By observation sinA+sinB+sinC=3
it will be only possible when A=B=C=90°
hence
cos90=0
CosA+cosB+cosC=0+0+0=0
12.
In the first quadrant: The sine and cosine are the same at 45°. Above that the sine is larger, below that the cosine is larger. 10° is below 45°, so the cosine is larger and therefore cos10°-sin10° is positive.
13.
0
as cos90=0 that occur between cos1 ....cos179
and you know that anything multiplied by 0 =0
it will be only possible when A=B=C=90°
hence
cos90=0
CosA+cosB+cosC=0+0+0=0
12.
In the first quadrant: The sine and cosine are the same at 45°. Above that the sine is larger, below that the cosine is larger. 10° is below 45°, so the cosine is larger and therefore cos10°-sin10° is positive.
13.
0
as cos90=0 that occur between cos1 ....cos179
and you know that anything multiplied by 0 =0
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yup in 11th
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