By the law of cosines, the angle

satisfies

which reduces to

which converts to approximately 77 degrees (this can be done my multiplying by 180 and dividing by pi).
Given: sin theta = 2/5. This tells us that the lengths of the opp side and the hyp are 2 and 5 respectively. The adj side is found using the Pyth. Thm.: 5^2-2^2= 25-4 = 21, so that the adj side is sqrt(21).
The double angle formula for the sine is sin 2theta = 2 sin theta *cos theta.
In this particular problem, the sine of 2theta is 2*(2/5)*[sqrt(21) / 5], or:
(4/25)*sqrt(21).
Step-by-step explanation:
5*(4x+8)=6*(2x+3)
20x+40=12x+18
20x _12x= 18_40
8x = _22
x=_22/8
x= _11/4
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