Use any method to multiply (3a + 2b - c)(a - b + 2c).
1 answer:
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Answer:
-
Step-by-step explanation:
Using the addition formula for cosine
cos(A + B) = cosAcosB - sinAsinB
Given sin A = - =
and in fourth quadrant, then
the triangle is a 7 - 24- 25 right triangle with adjacent side 24
In fourth quadrant cosine ratio is positive , thus
cos A = =
------------------------------------------------------------------
Given sin B = - =
and in third quadrant, then
the triangle is a 5- 12- 13 right triangle with adjacent side 5
In third quadrant cosine ratio is negative, thus
cos B = = -
Thus
cosAcosB - sinAsinB
= ( × -
) - (-
× -
)
= - -
= -