The minimum value of f(x)=cosec square x+25sec square x=
a) 26
b) 36
c) 24
d) 1
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26 is the answer I think
Answered by
1
Answer:
Let f(x) = cosec²x + 25sec²x
we know,
sec²x - tan²x = 1 , sec²x = 1 + tan²x
cosec²x - cot²x = 1 , cosec²x = 1 + cot²x
then, f(x) = 1 + cot²x + 25(1 + tan²x)
= 1 + cot²x + 25 + 25tan²x
f(x) = 26 + cot²x + 25tan²x
we know, if a and b are two positive terms,
then, AM ≥ GM
here cot²x and 25tan²x are two positive terms,
so, (cot²x + 25tan²x)/2 ≥ √{25tan²x.cot²x}
cot²x + 25tan²x ≥ 2 × √{25 × 1} = 2×5 = 10
cot²x + 25tan²x ≥ 10
add 26 both sides,
cot²x + 25tan²x + 26 ≥ 10 + 26 = 36
f(x) = cot²x + 25tan²x + 26 ≥ 36
hence, minimum value of f(x) is 36 .
hence, minimum value of cosec²x + 25sec²x = 36
hope it help you
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