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Given that 
sin x=(1)/(sqrt2) and 
cos y=(3)/(sqrt10), and that angles 
x and 
y are both in Quadrant I, find the exact value of 
sin(x-y), in simplest radical form.
Answer:

Given that sinx=12 \sin x=\frac{1}{\sqrt{2}} and cosy=310 \cos y=\frac{3}{\sqrt{10}} , and that angles x x and y y are both in Quadrant I, find the exact value of sin(xy) \sin (x-y) , in simplest radical form.\newlineAnswer:

Full solution

Q. Given that sinx=12 \sin x=\frac{1}{\sqrt{2}} and cosy=310 \cos y=\frac{3}{\sqrt{10}} , and that angles x x and y y are both in Quadrant I, find the exact value of sin(xy) \sin (x-y) , in simplest radical form.\newlineAnswer:
  1. Apply Sine Subtraction Formula: Use the sine subtraction formula: sin(xy)=sin(x)cos(y)cos(x)sin(y)\sin(x - y) = \sin(x)\cos(y) - \cos(x)\sin(y). We already know sin(x)=12\sin(x) = \frac{1}{\sqrt{2}} and cos(y)=310\cos(y) = \frac{3}{\sqrt{10}}. Next, we need to find cos(x)\cos(x) and sin(y)\sin(y).
  2. Find cos(x)\cos(x) and sin(y)\sin(y): Since xx is in Quadrant I and sin(x)=12\sin(x) = \frac{1}{\sqrt{2}}, we can use the Pythagorean identity sin2(x)+cos2(x)=1\sin^2(x) + \cos^2(x) = 1 to find cos(x)\cos(x).
    cos2(x)=1sin2(x)\cos^2(x) = 1 - \sin^2(x)
    cos2(x)=1(12)2\cos^2(x) = 1 - \left(\frac{1}{\sqrt{2}}\right)^2
    cos2(x)=112\cos^2(x) = 1 - \frac{1}{2}
    cos2(x)=12\cos^2(x) = \frac{1}{2}
    sin(y)\sin(y)00, since cos(x)\cos(x) is positive in Quadrant I.
  3. Substitute Values: Similarly, since yy is in Quadrant I and cos(y)=310\cos(y) = \frac{3}{\sqrt{10}}, we use the Pythagorean identity sin2(y)+cos2(y)=1\sin^2(y) + \cos^2(y) = 1 to find sin(y)\sin(y).sin2(y)=1cos2(y)\sin^2(y) = 1 - \cos^2(y)sin2(y)=1(310)2\sin^2(y) = 1 - \left(\frac{3}{\sqrt{10}}\right)^2sin2(y)=1910\sin^2(y) = 1 - \frac{9}{10}sin2(y)=110\sin^2(y) = \frac{1}{10}sin(y)=110=110\sin(y) = \sqrt{\frac{1}{10}} = \frac{1}{\sqrt{10}}, since sin(y)\sin(y) is positive in Quadrant I.
  4. Simplify Expression: Now we can substitute the values into the sine subtraction formula:\newlinesin(xy)=sin(x)cos(y)cos(x)sin(y)\sin(x - y) = \sin(x)\cos(y) - \cos(x)\sin(y)\newlinesin(xy)=(12)(310)(12)(110)\sin(x - y) = \left(\frac{1}{\sqrt{2}}\right)\left(\frac{3}{\sqrt{10}}\right) - \left(\frac{1}{\sqrt{2}}\right)\left(\frac{1}{\sqrt{10}}\right)
  5. Rationalize Denominator: Simplify the expression:\newlinesin(xy)=32101210\sin(x - y) = \frac{3}{\sqrt{2}\sqrt{10}} - \frac{1}{\sqrt{2}\sqrt{10}}\newlinesin(xy)=31210\sin(x - y) = \frac{3 - 1}{\sqrt{2}\sqrt{10}}\newlinesin(xy)=2210\sin(x - y) = \frac{2}{\sqrt{2}\sqrt{10}}
  6. Rationalize Denominator: Simplify the expression:\newlinesin(xy)=32101210\sin(x - y) = \frac{3}{\sqrt{2}\sqrt{10}} - \frac{1}{\sqrt{2}\sqrt{10}}\newlinesin(xy)=31210\sin(x - y) = \frac{3 - 1}{\sqrt{2}\sqrt{10}}\newlinesin(xy)=2210\sin(x - y) = \frac{2}{\sqrt{2}\sqrt{10}}Rationalize the denominator:\newlinesin(xy)=2210×210210\sin(x - y) = \frac{2}{\sqrt{2}\sqrt{10}} \times \frac{\sqrt{2}\sqrt{10}}{\sqrt{2}\sqrt{10}}\newlinesin(xy)=22102×10\sin(x - y) = \frac{2\sqrt{2}\sqrt{10}}{2\times10}\newlinesin(xy)=21010\sin(x - y) = \frac{\sqrt{2}\sqrt{10}}{10}\newlinesin(xy)=2010\sin(x - y) = \frac{\sqrt{20}}{10}\newlinesin(xy)=4×510\sin(x - y) = \frac{\sqrt{4\times5}}{10}\newlinesin(xy)=2510\sin(x - y) = \frac{2\sqrt{5}}{10}\newlinesin(xy)=55\sin(x - y) = \frac{\sqrt{5}}{5}

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