What is the value of sec (t), if tan(t) = 1⁄3?

- (a)

- (b)

- (c)

- (d)

Answer
Why
Correct — C. The stem gives tan t = 1⁄3 and asks for sec t, so use the identity that bridges those two: sec²t = 1 + tan²t.
sec²t = 1 + tan²t
= 1 + (1⁄3)² = 1 + 1⁄9
= 10⁄9
Square-root the top and the bottom:
sec t = √10⁄√9
= √10⁄3 → option (c)
The triangle route agrees. Label opposite = 1 and adjacent = 3, so the hypotenuse is √(1² + 3²) = √10, and sec t = hypotenuse⁄adjacent = √10⁄3.
Why the others are wrong
- (a)Below 1, so it cannot be a secant at all. |sec t| ≥ 1 always, because sec t = 1⁄cos t and |cos t| ≤ 1. √3⁄3 ≈ 0.58 is the value of tan 30°, which nothing here asks for.
- (b)Ruled out by the same test — 2√2⁄3 = √(8⁄9) ≈ 0.94, again below 1. It is what you get by reading the given 1⁄3 as sin t and computing cos t = √(1 − 1⁄9).
- (d)Right numerator, unfinished denominator. Stopping at √10⁄9 ≈ 0.35 roots only the top and lands below 1 again — both parts must be rooted: √10⁄√9 = √10⁄3.
Concept
Once any one ratio of an acute angle is known, every other ratio is fixed. The shortest bridge from tan to sec is 1 + tan²t = sec²t, which is just sin²t + cos²t = 1 divided through by cos²t.
The triangle picture makes it concrete. tan t = opposite⁄adjacent = 1⁄3 lets you label the two legs 1 and 3, and Pythagoras fixes the hypotenuse at √10.
Every remaining ratio then reads straight off that same triangle: sec t = √10⁄3, cos t = 3⁄√10, sin t = 1⁄√10, cosec t = √10.
Strictly, tan t = 1⁄3 also holds in the third quadrant, where sec t = −√10⁄3.
All four options here are positive, so the intended t is acute. Read SSC trigonometry items as first-quadrant unless the paper states a quadrant or a range.
Key facts
- 1 + tan²t = sec²t, obtained by dividing sin²t + cos²t = 1 through by cos²t.
- 1 + cot²t = cosec²t, the same identity divided by sin²t instead.
- |sec t| ≥ 1 and |cosec t| ≥ 1 always, so any option strictly between −1 and 1 can be struck out before calculating.
- For acute t with tan t = p⁄q, the hypotenuse is √(p² + q²), so sec t = √(p² + q²)⁄q.
Study next
Common traps
- Square-rooting only the numerator of sec²t = 10⁄9 and answering √10⁄9.
- Reading the given 1⁄3 as sin t or cos t rather than tan t.
- Rationalising out of habit — √10⁄3 already has a rational denominator.
SSC hands you one ratio and asks for another, choosing numbers that make the third side a surd such as √10 or √13 so the answer looks harder than the work is. The same stem returns as 'find sec t + tan t' or 'sec t − tan t', which the identical triangle answers.
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