Q. Given that tanA=2 and sinB=415, and that angles A and B are both in Quadrant I, find the exact value of sin(A−B), in simplest radical form.Answer:
Apply Angle Subtraction Formula: We will use the angle subtraction formula for sine, which is sin(A−B)=sin(A)cos(B)−cos(A)sin(B). To use this formula, we need to find sin(A), cos(A), and cos(B).
Find sin(A), cos(A), cos(B): Since tanA=2 and we are in Quadrant I, we can create a right triangle where the opposite side to angle A is 2 and the adjacent side is 1. Using the Pythagorean theorem, the hypotenuse is 12+22=5. Therefore, sin(A)=hypotenuseopposite=52. To rationalize, we multiply by 55 to get sin(A)=525.
Use Pythagorean Identity for sin(B): Using the same triangle, cos(A)=hypotenuseadjacent=51. Rationalizing, we get cos(A)=55.
Calculate cos(B): We are given sinB=415. To find cos(B), we use the Pythagorean identity sin2(B)+cos2(B)=1. Substituting sinB, we get (415)2+cos2(B)=1. Simplifying, we get 4125+cos2(B)=1.
Substitute into Angle Subtraction Formula: Subtract 4125 from both sides to solve for cos2(B): cos2(B)=1−4125. This simplifies to cos2(B)=(4141)−(4125)=4116. Taking the square root, cos(B)=4116=414. Since B is in Quadrant I, cos(B) is positive, so cos(B)=414. Rationalizing, we get cos(B)=41441.
Combine Terms: Now we have sin(A)=525, cos(A)=55, and cos(B)=41441. We can substitute these into the angle subtraction formula: sin(A−B)=(525)(41441)−(55)(415).
Rewrite Fraction: Multiplying the terms, we get sin(A−B)=2058205−4155. To combine these terms, we need a common denominator, which is 205.
Subtract Fractions: We rewrite (55/41) as (255/205) to have the same denominator. Now, sin(A−B)=(8205/205)−(255/205).
Final Result: Subtracting the fractions, we get sin(A−B)=2058205−255. This is the exact value of sin(A−B) in simplest radical form.
More problems from Find trigonometric ratios using multiple identities