Question

cos (-780°) का मान ........​

Answer 1

$\large \sf \underline{ \underline{ \: Solution : \: \: \: }}$

$\sf \implies Cos \: ( - 780 ) \\ \\ \sf \implies</p><p>Cos \: ( 780 ) \\ \\ \sf \implies</p><p>Cos \: ( 360 × 2 + 60 ) \\ \\ \sf \implies</p><p>Cos \: ( 60 ) \\ \\ \sf \implies </p><p> \frac{1}{2}$

$\large \sf \underline{ \underline{ \:Remmember : \: \: \: }}$

$\sf \star \: \: Cos \: ( - \: \theta) = Cos \: ( \theta) \\ \\ \sf \star \: \: Cos \: ( 360 \times n + \theta) = Cos \: ( \theta)$

Answer 2

Cos(-780) = Cos(780)

[as cos(-theta)= cos(theta)]

Cos(2×360+60)

Cos(60)

1/2....