Please help me with this problem if you can! Thank you.
1 answer:
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9514 1404 393
Answer:
77/85
Step-by-step explanation:
<u>Given</u>:
cos(A) = 4/5
sin(B) = 15/17
<u>Find</u>:
cos(A-B)
<u>Solution</u>:
From your knowledge of Pythagorean triples, you know that one of them is (3, 4, 5) and another is (8, 15, 17). Using your imagination, or by drawing the triangles, you can determine the needed trig functions to be ...
sin(A) = 3/5
cos(B) = 8/17
__
Alternatively, you can use the Pythagorean identity to find ...
sin(A) = √(1 -cos²(A)) = √(1 -(4/5)²) = √(9/25) = 3/5
cos(B) = √(1 -sin²(B)) = √(1 -(15/17)²) = √(64/289) = 8/17
__
Then application of the angle difference formula is straightforward.
cos(A -B) = cos(A)cos(B) +sin(A)sin(B)
cos(A -B) = (4/5)(8/17) +(3/5)(15/17) = (32 +45)/85
cos(A -B) = 77/85
_____
Some graphing calculators can express the result ...
cos(arccos(4/5) -arcsin(15/17)) ≈ 0.90588235294
... as the fraction 77/85
You divide the double digit divisor into the dividend. If the dividend is a double digit number too then you add a decimal and a zero to the dividend
