Tag: using trigonometric tables

Questions Related to using trigonometric tables

Multiple choice using trigonometric tables trigonometric ratios of some specific angles trigonometric identities trigonometry maths

$ \sqrt { 3 } \ cosec 20 ^ { \circ } - \sec 20 ^ { \circ }$  is equal to :

  1. $2$
  2. $2 \sin 20 ^ { \circ } / \sin 40 ^ { \circ }$
  3. $4$
  4. $4 \sin 20 ^ { \circ } / \sin 40 ^ { \circ }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Expressing csc(20) as 1/sin(20) and sec(20) as 1/cos(20), the expression becomes sqrt(3)/sin(20) - 1/cos(20). Combining terms and using the sine subtraction formula with a factor of 2 yields 4, identical to the standard identity reduction.

Multiple choice using trigonometric tables trigonometric ratios of some specific angles trigonometric identities trigonometry maths

$\tan 5\tan 25\tan 30\tan 65 \tan 85$ is equal to

  1. $3$
  2. $\surd {3}$
  3. $1$
  4. $\dfrac {1}{\surd {3}}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using complementary angle properties, tan(85) = cot(5) = 1/tan(5) and tan(65) = cot(25) = 1/tan(25). Thus, tan(5) and tan(85) cancel out, as do tan(25) and tan(65). We are left with tan(30 degrees), which equals 1 / sqrt(3).

Multiple choice using trigonometric tables trigonometric ratios of some specific angles trigonometric identities trigonometry maths

$\tan 20 ^ { \circ } + \tan 40 ^ { \circ } + \sqrt { 3 } \tan 20 ^ { \circ } \tan 40 ^ { \circ }$  is equal to

  1. $\dfrac { \sqrt { 3 } } { 2 }$
  2. $\dfrac { \sqrt { 3 } } { 4 }$
  3. $\sqrt { 3 }$
  4. $1$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

From the identity tan(A + B) = (tan(A) + tan(B)) / (1 - tan(A)tan(B)), let A = 20 degrees and B = 40 degrees, so tan(60 degrees) = sqrt(3) = (tan(20) + tan(40)) / (1 - tan(20)tan(40)). Cross-multiplying gives tan(20) + tan(40) = sqrt(3) - sqrt(3)tan(20)tan(40), which rearranges to tan(20) + tan(40) + sqrt(3)tan(20)tan(40) = sqrt(3).

Multiple choice using trigonometric tables trigonometric ratios of some specific angles trigonometric identities trigonometry maths

If $\alpha =685^o$, then $(\cos\alpha -\sin\alpha)$ is equivalent to?

  1. $-\cos 35^o-\sin 35^o$
  2. $-\cos 35^o +\sin 35^o$
  3. $\cos 35^o-\sin 35^o$
  4. $\cos 35^o+\sin 35^o$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Reduce alpha = 685 degrees modulo 360 degrees: 685 - 2*360 = 685 - 720 = -35 degrees. Then cos(-35 degrees) - sin(-35 degrees) = cos(35 degrees) + sin(35 degrees) since cosine is even and sine is odd.