Question

The value of cos2 225° + cos2 135° is

Answer 1

Answer:

0 is the correct Answer good by

Answer 2

Answer:

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Step-by-step explanation:

so cos 225 can be written as

cos(180+45)

do as we know that whenever there is π in any trigonometric ratio,then that ratio remains unchanged

hence cos 225=cos 45

so cos 45=1/√2

but as 225 lies in 3rd quadrant and as we know that in third quadrant except tan and cot all other trigonometric ratios are negative

hence cos 225=-1/√2

moreover similarly cos 135 can be written as

cos(180-45)=cos 45

so thus similarly as 135 lies in quadrant 2 and except sin and cosec all other trigonometric ratios are negative

cos 135=-1/√2

thus then

cos²225+cos² 135

=(-1√2)²+(-1/√2)²

=1/2+1/2

=1+1/2

=2/2

=1

hence cos²225+cos² 135=1