For each t ∈R, let [t] be the greatest integer less than or equal to t. Then
does not exist (in R)
is equal to 0
is equal to 15
is equal to 120
D.
is equal to 120
If 5(tan2x – cos2x) = 2cos 2x + 9, then the value of cos4x is
-7/9
-3/5
1/3
1/3
A.
-7/9
⇒5(1 – t – t2) = t(4t + 7)
⇒ 9t2 + 12t – 5 = 0
⇒ 9t2 + 15t – 3t – 5 = 0
⇒ (3t – 1) (3t + 5) = 0
⇒ t = t/3 as t≠-5/3.
cos2x = 2(1/3)-1 = -1/3