NIMCET 2013 — Mathematics PYQ
NIMCET | Mathematics | 2013If sinx+acosx=b, then what is the expression for ∣asinx−cosx∣ in terms of a and b?
Choose the correct answer:
- A.
a2−b2−1
- B.
a2+b2−1
a2−b2+1
Explanation
Solution
1. Set up the equations:
Let the required expression be y:
y=∣asinx−cosx∣
The given equation is:
b=sinx+acosx
2. Square both equations:
First equation squared:
b2=(sinx+acosx)2
b2=sin2x+a2cos2x+2asinxcosx…(i)
Second equation squared:
y2=(asinx−cosx)2
y2=a2sin2x+cos2x−2asinxcosx…(ii)
3. Add equations (i) and (ii):
b2+y2=(sin2x+a2cos2x+2asinxcosx)+(a2sin2x+cos2x−2asinxcosx)
b2+y2=sin2x+cos2x+a2sin2x+a2cos2x
b2+y2=(sin2x+cos2x)+a2(sin2x+cos2x)
4. Use the identity sin2x+cos2x=1:
b2+y2=1+a2(1)
b2+y2=1+a2
5. Solve for y:
y2=a2−b2+1
y=a2−b2+1
Explanation
Solution
1. Set up the equations:
Let the required expression be y:
y=∣asinx−cosx∣
The given equation is:
b=sinx+acosx
2. Square both equations:
First equation squared:
b2=(sinx+acosx)2
b2=sin2x+a2cos2x+2asinxcosx…(i)
Second equation squared:
y2=(asinx−cosx)2
y2=a2sin2x+cos2x−2asinxcosx…(ii)
3. Add equations (i) and (ii):
b2+y2=(sin2x+a2cos2x+2asinxcosx)+(a2sin2x+cos2x−2asinxcosx)
b2+y2=sin2x+cos2x+a2sin2x+a2cos2x
b2+y2=(sin2x+cos2x)+a2(sin2x+cos2x)
4. Use the identity sin2x+cos2x=1:
b2+y2=1+a2(1)
b2+y2=1+a2
5. Solve for y:
y2=a2−b2+1
y=a2−b2+1
