Question

If \[A = {30^ \circ }\]and\[B = {60^ \circ }\], then \[cos\left( {A + B} \right) = cosAcosB-sinAsinB\]. If the above statement is true, write \[1\] and if false then write \[0\].

Answer 1

Hint:Start by putting the values of $A$ and $B$ and in the formula and solve by taking the trigonometric values.

Complete step-by-step answer:
L.H.S
 \[ \Rightarrow cos\left( {A + B} \right)\]
\[ \Rightarrow \;cos\left( {{{60}^ \circ } + {{30}^ \circ }} \right)\]
\[ \Rightarrow \;cos{90^ \circ } = {\text{ }}0\]
R.H.S
\[ \Rightarrow cosAcosB-sinAsinB\]
\[ \Rightarrow \;cos{60^ \circ }cos{30^ \circ }-sin{0^ \circ }sin{30^ \circ }\]
\[\frac{{\sqrt 3 }}{4} - \frac{{\sqrt 3 }}{4} = 0\]
Since, LHS=RHS
Therefore, the answer is TRUE which in this question is equal to \[1\].
Note: We started by assigning the values of A and B in the given equation and then simplifying to get the answer.