A postcard is 4 inches shorter than an envelope. The envelope is 10 inches long. How long is the postcard? The diagram below cou
2 answers:
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Cos(x) = sin(x + 20o) Use the double cos angle formula
Cos(x) = sin(x)*cos(20) + cos(x)*sin(20) Divide through by cos(x). Tanx = sin(x)/cos(x)
1 = tan(x)*cos(20) + sin(20) Subtract sin(20) from both sides.
1 - sin(20) = tan(x)*cos(20) Calculate the value of 1 - sin(20)
0.65798 = tan(x) * 0.939692 Divide by cos(20)
tan(x) = 0.65795/0.939692
tan(x) = 0.70021 Take the inverse of 0.7) = tan(x)
x = tan-1(0.70021)
x = 35 degrees as expected.
Problem Two
The easiest way to do this is to pick random values and try it. The two acute angles are complementary. So 25 and 65 are random enough.
Let A = 25
Let C = 65
A
Tan(25) = sin(25)/sin(65) ; tan(25) = 0.4663.
sin(25)/sin(65) = 0.4663 Answer
B
Sin(90 - C) = Sin(A)
Tan(90 - A) = Tan(C)
So the question becomes Cos(A) = Tan(C) / sin(A)
Cos(25) = Tan(65)/Sin(25)
0.906 = ? 5.07 This statement isn't true.
C
Sin(65) = Cos(25)/Tan(65)
.906 = 0.4226 C is not the correct answer.
D
D isn't true. The tan does not relate that away. You can find it for yourself.
Cos(A) = Tan(C) You should get 0.906 = 2.14
E
Sin(C) = Cos(A) / Tan(A) I'll leave you to show this is wrong.
Problem 3
The diagram below is for this problem. Cos(x) = 50/100 = 0.5
x = cos-1(0.5)
x = 60 degrees.
Part 2
Sin(60) = opposite / hypotenuse
opposite = sin(60) * hypotenuse
opposite = 86.61 Be sure and round this to whatever the question says to round it to.
