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Given that 
cos A=(sqrt2)/(3) and 
cos B=(sqrt30)/(6), and that angles 
A and 
B are both in Quadrant I, find the exact value of 
sin(A-B), in simplest radical form.
Answer:

Given that cosA=23 \cos A=\frac{\sqrt{2}}{3} and cosB=306 \cos B=\frac{\sqrt{30}}{6} , and that angles A A and B B are both in Quadrant I, find the exact value of sin(AB) \sin (A-B) , in simplest radical form.\newlineAnswer:

Full solution

Q. Given that cosA=23 \cos A=\frac{\sqrt{2}}{3} and cosB=306 \cos B=\frac{\sqrt{30}}{6} , and that angles A A and B B are both in Quadrant I, find the exact value of sin(AB) \sin (A-B) , in simplest radical form.\newlineAnswer:
  1. Use Cosine Subtraction Formula: Use the cosine subtraction formula to find sin(AB)\sin(A-B). The cosine subtraction formula is cos(AB)=cos(A)cos(B)+sin(A)sin(B)\cos(A-B) = \cos(A)\cos(B) + \sin(A)\sin(B). Since we are looking for sin(AB)\sin(A-B), we need to use the sine and cosine values to find sin(A)\sin(A) and sin(B)\sin(B) first.
  2. Find Sine Values: Find sin(A)\sin(A) and sin(B)\sin(B) using the Pythagorean identity.\newlineThe Pythagorean identity is sin2(θ)+cos2(θ)=1\sin^2(\theta) + \cos^2(\theta) = 1.\newlineFor angle A:\newlinesin2(A)=1cos2(A)\sin^2(A) = 1 - \cos^2(A)\newlinesin2(A)=1(23)2\sin^2(A) = 1 - (\frac{\sqrt{2}}{3})^2\newlinesin2(A)=129\sin^2(A) = 1 - \frac{2}{9}\newlinesin2(A)=9929\sin^2(A) = \frac{9}{9} - \frac{2}{9}\newlinesin2(A)=79\sin^2(A) = \frac{7}{9}\newlinesin(A)=79\sin(A) = \sqrt{\frac{7}{9}}\newlinesin(A)=73\sin(A) = \frac{\sqrt{7}}{3}\newlineFor angle B:\newlinesin(B)\sin(B)00\newlinesin(B)\sin(B)11\newlinesin(B)\sin(B)22\newlinesin(B)\sin(B)33\newlinesin(B)\sin(B)44\newlinesin(B)\sin(B)55\newlinesin(B)\sin(B)66\newlinesin(B)\sin(B)77
  3. Apply Sine Subtraction Formula: Apply the sine subtraction formula. The sine subtraction formula is sin(AB)=sin(A)cos(B)cos(A)sin(B)\sin(A-B) = \sin(A)\cos(B) - \cos(A)\sin(B). Substitute the values we found for sin(A)\sin(A), cos(A)\cos(A), sin(B)\sin(B), and cos(B)\cos(B): sin(AB)=(7/3)(30)/6(2)/3(6)/6\sin(A-B) = (\sqrt{7}/3)\cdot(\sqrt{30})/6 - (\sqrt{2})/3\cdot(\sqrt{6})/6
  4. Simplify Expression: Simplify the expression.\newlinesin(AB)=730362636\sin(A-B) = \frac{\sqrt{7}\cdot\sqrt{30}}{3\cdot6} - \frac{\sqrt{2}\cdot\sqrt{6}}{3\cdot6}\newlinesin(AB)=210181218\sin(A-B) = \frac{\sqrt{210}}{18} - \frac{\sqrt{12}}{18}\newlinesin(AB)=2101218\sin(A-B) = \frac{\sqrt{210} - \sqrt{12}}{18}\newlinesin(AB)=2102318\sin(A-B) = \frac{\sqrt{210} - 2\cdot\sqrt{3}}{18}\newlinesin(AB)=2102318\sin(A-B) = \frac{\sqrt{210} - 2\cdot\sqrt{3}}{18}
  5. Simplify Radicals: Simplify the radicals if possible. 210\sqrt{210} can be simplified to 2×3×5×7=2×3×5×7=6×35\sqrt{2\times3\times5\times7} = \sqrt{2}\times\sqrt{3}\times\sqrt{5}\times\sqrt{7} = \sqrt{6}\times\sqrt{35} So, sin(AB)=(6×352×3)/18\sin(A-B) = (\sqrt{6}\times\sqrt{35} - 2\times\sqrt{3})/18 sin(AB)=(6×35)/18(2×3)/18\sin(A-B) = (\sqrt{6}\times\sqrt{35})/18 - (2\times\sqrt{3})/18 sin(AB)=(210)/18(2×3)/18\sin(A-B) = (\sqrt{210})/18 - (2\times\sqrt{3})/18 We already simplified 210\sqrt{210} earlier, so this step does not change the expression.

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