Answer:
Cos(15) = Cos(45-30)
Sin(15) = Sin(45-30)
Cos(45-30) - Sin(45-30)
Simplifying both brackets
Recall
Cos(A+B) = CosACosB - SinASinB (For cosine... The sign is always the opposite during expansion. If you look... Cos(A+B) became negative during its expansion;So if It was Cos(A–B)... Its expansion is CosACosB + SinASinB)]
Sin(A+B) = SinACosB + CosASinB
Now let's go!
Cos(45-30) = Cos45Cos30 + Sin45Sin30
From Trig
Cos45 = 1/√2
Cos30 = √3/2
Sin45 = 1/√2
Sin30 = 1/2
Substituting
Cos(45-30) = (1/√2).(√3/2) + (1/√2).(1/2)
= √3/(2√2) + 1/(2√2)
= 1 + √3/(2√2).
For
Sin(45 - 30)
= Sin45cos30 – Cos45Sin30
= (1/√2).(√3/2) – (1/√2).(1/2)
= √3/(2√2) – 1/2√2
= √3 – 1/(2√2)
So the question was
Cos15 - Sin15
Substituting...
1 + √3 / 2√2 – (√3 - 1)/ 2√2
When the Minus interacts with the parenthesis
We have
1 + √3 - √3 + 1 / (2√2)
= 2/2√2
= 1/√2.
THE ANSWER IS 1/√2 AND NOT 1/2.
YOU CAN VERIFY THIS WITH YOUR CALCULATOR ALSO.
YOU'LL HAVE 0.7071 WHICH IS SAME AS 1/√2.
HAVE A GREAT DAY!
