If sinθ+cscθ=5, then the value of sin
3
θ+csc
3
θ is:
- A110
- B115
- C125
- D140
Solution & Step-by-step Explanation
Let x=sinθ. Since cscθ=
sinθ
1
, we can write cscθ=
x
1
.
The given equation is:
x+
x
1
=5
We need to find the value of sin
3
θ+csc
3
θ=x
3
+
x
3
1
.
Using the algebraic identity:
(x+
x
1
)
3
=x
3
+
x
3
1
+3(x+
x
1
)
Substitute the value x+
x
1
=5:
5
3
=x
3
+
x
3
1
+3(5)
125=x
3
+
x
3
1
+15
x
3
+
x
3
1
=125−15=110
sinθ
1
, we can write cscθ=
x
1
.
The given equation is:
x+
x
1
=5
We need to find the value of sin
3
θ+csc
3
θ=x
3
+
x
3
1
.
Using the algebraic identity:
(x+
x
1
)
3
=x
3
+
x
3
1
+3(x+
x
1
)
Substitute the value x+
x
1
=5:
5
3
=x
3
+
x
3
1
+3(5)
125=x
3
+
x
3
1
+15
x
3
+
x
3
1
=125−15=110