If tan θ + sec θ = 7, θ being acute, then the value of 5 sin θ is:
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Correct answer: D
Explanation
The correct answer is option 4 i.e.
Given:
tanθ + secθ = 7
Concept used:
1. sec2θ - tan2θ = 1
2. tanα = sinα/cosα
3. secα = 1/cosα
Calculation:
tanθ + secθ = 7 ....(1)
We know,
sec²θ - tan2θ = 1
⇒ (secθ - tanθ) (secθ + tanθ) = 1
⇒ (secθ - tanθ) × 7 = 1 (From 1)
⇒ (secθ - tanθ) = 1/7 ...(2)
By adding (1) and (2) we get,
⇒ 2 secθ = 7 + 1/7 = 50/7
⇒ secθ = 25/7
By subtracting (1) and (2) we get,
⇒ 2 tanθ = 7 - 1/7 = 48/7
⇒ tanθ = 24/7
secθ = 25/7 and tanθ= 24/7
So, sinθ
⇒ tanθ / secθ
⇒ 24/7 / 25 / 7
⇒ 24/25
Now, 5sinθ
⇒ 5sinθ = 5 × 24 / 25 = 24/5
:. The value of 5 sinθ is 24/5