Question

Cos s=-2/5 and sin t=4/5, s and t are in quadrant 4 find cos(s+t) and cos(s-t)

Answer 1

With Cos s=-2/5 and sin t=4/5, s and t are in quadrant 4,  cos(s+t) and cos(s-t) is mathematically given as

cos(s+t)= 0.493

cos(s-t)= 0.97321

What are the values of cos(s+t) and cos(s-t)?

Question Parameter(s):

Cos s=-2/5 and sin t=4/5, s and t are in quadrant 4

Generally, the equation for the s and t as functions of the 4 qudrants is mathematically given as

cos(s+t) = cos(s)*cos(t) - sin(s)*sin(t)

Therefore

cos(s+t)= -4/5 * $(-\sqrt{21}$/5) - (-3/5)*(-2/5)

cos(s+t)= 4*$\sqrt{21}/$25 - 6/25

cos(s+t)= 0.493

In conclusion,

cos(s-t) = cos(s)*cos(t) + sin(s)*sin(t)

cos(s-t)= -4/5 * (-$\sqrt{21}/$5) + (-3/5)*(-2/5)

cos(s-t)= 4$*\sqrt{21}$/25 + 6/25

cos(s-t)= 0.97321

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