Cos² 2x = (1+cos 4x )/2
cos² 6x = (1+cos 12x)/2
subtract to get 1/2 (cos 4x - cos 12x )
= 1/2 (2 sin 4x sin 8x ) as cos A - cos B = 2 [ sin (A+B)/2 sin (A-B)/2 ]
so the answer
Answer:
4.11
Step-by-step explanation:
For the difference to be positive, when both the minuend and the subtrahend are positive, the former must be greater than the latter.
Therefore
minuend = 2 ⇒ subtrahend = 1 ← 1 number
minuend = 3 ⇒ subtrahend = 1,2 ← 2 numbers
minuend = 4 ⇒ subtrahend = 1,2,3 ← 3 numbers
minuend = 5 ⇒ subtrahend = 1,2,3,4 ← 4 numbers
minuend = 6 ⇒ subtrahend = 1,2,3,4,5 ← 5 numbers
1+2+3+4+5=<u>15</u>
