Question

Findℒ{f(t)}by first using a trigonometric identity. (Write your answer as a function of s.)f(t) = 12 cost −π6

Answer 1

Answer:

$L(f(t)) = \dfrac{6}{S^2+1} [\sqrt{3} \ S +1 ]$

Step-by-step explanation:

Given that:

$f(t) = 12 cos (t- \dfrac{\pi}{6})$

recall that:

cos (A-B) = cos AcosB + sin A sin B

∴

$f(t) = 12 [cos\ t \ cos \dfrac{\pi}{6}+ sin \ t \ sin \dfrac{\pi}{6}]$

$f(t) = 12 [cos \ t \ \dfrac{3}{2}+ sin \ t \ sin \dfrac{1}{2}]$

$f(t) = 6 \sqrt{3} \ cos \ (t) + 6 \ sin \ (t)$

$L(f(t)) = L ( 6 \sqrt{3} \ cos \ (t) + 6 \ sin \ (t) ]$

$L(f(t)) = 6 \sqrt{3} \ L [cos \ (t) ] + 6\ L [ sin \ (t) ]$

$L(f(t)) = 6 \sqrt{3} \dfrac{S}{S^2 + 1^2}+ 6 \dfrac{1}{S^2 +1^2}$

$L(f(t)) = \dfrac{6 \sqrt{3} +6 }{S^2+1}$

$L(f(t)) = \dfrac{6( \sqrt{3} \ S +1 }{S^2+1}$

$L(f(t)) = \dfrac{6}{S^2+1} [\sqrt{3} \ S +1 ]$