Q. By expressing 3sinx+3cosx in the form Asin(x+α), solve3sinx+3cosx=3, for 0≤x≤2π.
Use Trigonometric Identity: We want to express 3sin(x)+3cos(x) in the form Asin(x+α). To do this, we will use the identity sin(x+α)=sin(x)cos(α)+cos(x)sin(α).
Match Coefficients: Let Asin(x+α)=A(sin(x)cos(α)+cos(x)sin(α)). We want to match the coefficients of sin(x) and cos(x) to those in 3sin(x)+3cos(x).
Solve Equations for A: Matching coefficients, we get Acos(α)=3 and Asin(α)=3. We can solve these two equations to find A and α.
Find A Using Pythagorean Identity: To find A, we use the Pythagorean identity: A2=(Acos(α))2+(Asin(α))2. Substituting the values we have A2=(3)2+32=3+9=12.
Find A and A: Taking the square root of both sides, we get A=12=23.
Express in Desired Form: To find α, we take the ratio of the two equations: tan(α)=Acos(α)Asin(α)=33=3.
Isolate sin(x+α): Using the arctan function, we find α=arctan(3). Since we are looking for solutions in the interval [0,2π], we consider the principal value of arctan(3), which is π/3.
Find Solutions for sin(y): Now we have expressed 3sin(x)+3cos(x) as 23sin(x+π/3). We can now solve the equation 23sin(x+π/3)=3.
Substitute x+α for y: Divide both sides by 23 to isolate sin(x+π/3): sin(x+π/3)=233=21.
Solve for x: We look for solutions to sin(x+3π)=21. The solutions to sin(y)=21 are y=6π+2kπ and y=65π+2kπ, where k is an integer.
Check Solutions in Interval: Substitute x+3π for y: x+3π=6π+2kπ or x+3π=65π+2kπ. We solve for x in each case.
Final Solutions: For the first equation: x=6π−3π+2kπ=−6π+2kπ. For the second equation: x=65π−3π+2kπ=2π+2kπ.
Final Solutions: For the first equation: x=6π−3π+2kπ=−6π+2kπ. For the second equation: x=65π−3π+2kπ=2π+2kπ.We need to find the values of x in the interval [0,2π]. For the first equation, x=−6π is not in the interval, but x=−6π+2π=611π is. For the second equation, x=2π is in the interval.
Final Solutions: For the first equation: x=6π−3π+2kπ=−6π+2kπ. For the second equation: x=65π−3π+2kπ=2π+2kπ.We need to find the values of x in the interval [0,2π]. For the first equation, x=−6π is not in the interval, but x=−6π+2π=611π is. For the second equation, x=2π is in the interval.The solutions to the equation 3sin(x)+3cos(x)=3 in the interval [0,2π] are x=611π and x=2π.
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