Q9 of 104 Page 193

State whether the following are true or false. Justify your answer:

(1) The value of sinθ increases as θ increases from 0 to 90.


(2) sinθ = cosθ for all value ofθ.


(3) cos(A + B) = cosA + cosB


(4) tanA is not defined for A = 90.


(5) The value of cot increases as θ increases from 0 to 90.

(1) True

sin0 = 0


sin30 =


sin60 =


sin90 = 1


we can see its increasing with increase in the angle in the range 0–90.


(2) False


They are only equal at θ = 45, otherwise are not equal.


(3) False


Let A = B = 45


L.H.S


⇒ cos90 = 0


R.H.S


⇒ cos45 + cos45




(4) True



which is not defined


(5) False






it decreases with increase in θ.


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