1.

If cot theta = 5/4 then find the values of 5 sin theta + 3 cos theta / 5 sin theta - 2 cos theta

Answer»

➝Correct Question :

If cot\:\theta = \dfrac{3}{<klux>4</klux>}, then find the VALUE of:

5sin\:\theta + \dfrac{3cos\:\theta}{5sin\:\theta} - 2cos\:theta

➝ Find :

The value of :

\boxed{\mathtt{5sin\:\theta + \dfrac{3cos\:\theta}{5sin\:\theta} - 2cos\:theta}}

➝ Given :

The value of cot\:\theta

\rightarrow cot\:\theta = \dfrac{3}{4}

➝ We Know :

The trigonometrical identity of

  • cot\:\theta = \dfrac{b}{p}

  • sin\:\theta = \dfrac{p}{h}

  • cos\:\theta = \dfrac{b}{h}

Where,

  • b = base of the triangle
  • p = HEIGHT of triangle
  • h = hypotenuse of the triangle

Pythagoras theorem :

\boxed{\mathtt{h^{2} = p^{2} + b^{2}}}

Where,

  • h = Hypotenuse
  • p = height
  • b = base

➝ Concept :

According to the given information,that cot\:\theta = \dfrac{3}{4}, and the identity that cot\:\theta = \dfrac{b}{p} ,we got the base and height of the the triangle ..i.e,

  • Height = 4 units
  • base = 3 units

From the above information of base and height , we can find the value of Hypotenuse by the PYTHAGORAS theorem..

Pythagoras theorem :

\mathtt{h^{2} = p^{2} + b^{2}}

By using it ,and putting the value of height and base in the formula ,we get :

\mathtt{\Rightarrow h^{2} = 4^{2} + 3^{2}}

\mathtt{\Rightarrow h = \sqrt{4^{2} + 3^{2}}}

\mathtt{\Rightarrow h = \sqrt{16 + 9}}

\mathtt{\Rightarrow h = \sqrt{25}}

\mathtt{\Rightarrow h = 5 units}

Hence ,the hypotenuse of the triangle is 5 units.

By putting the value of different trigonometric identities , we can find the value of the given Equation :

  • sin\:\theta = \dfrac{4}{5}

(As sin\:\theta = \dfrac{p}{h})

  • cos\:\theta = \dfrac{3}{5}

(As cos\:\theta = \dfrac{b}{h})

➝ Solution :

We now know that :

  • sin\:\theta = \dfrac{4}{5}
  • cos\:\theta = \dfrac{3}{5}

Putting the value in the Equation ,

5sin\:\theta + \dfrac{3cos\:\theta}{5sin\:\theta} - 2cos\:theta

we get :

\mathtt{\Rightarrow 5 \times \dfrac{4}{5} + \dfrac{3 \times \dfrac{3}{5}}{5} \times \dfrac{4}{5} - 2 \times \dfrac{3}{5}}

\mathtt{\Rightarrow \cancel{5} \times \dfrac{4}{\cancel{5}} + \dfrac{3 \times \dfrac{3}{5}}{\cancel{5} \times \dfrac{4}{\cancel{5}}} - 2 \times \dfrac{3}{5}}

\mathtt{\Rightarrow 4 + \dfrac{\dfrac{9}{5}}{4}  - \dfrac{6}{5}}

\mathtt{\Rightarrow 4 + \dfrac{9}{5} \times 4  - \dfrac{6}{5}}

\mathtt{\Rightarrow 4 + \dfrac{36}{5} - \dfrac{6}{5}}

\mathtt{\Rightarrow \dfrac{20 + 36 - 6}{5}}

\mathtt{\Rightarrow \dfrac{56 - 6}{5}}

\mathtt{\Rightarrow \dfrac{50}{5}}

\mathtt{\Rightarrow \dfrac{\cancel{50}}{\cancel{5}}}

\mathtt{\Rightarrow 10}

Hence ,the value of 5sin\:\theta + \dfrac{3cos\:\theta}{5sin\:\theta} - 2cos\:theta is \mathtt{10}

➝ Extra Information :

Some Trigonometrical identities :

  • sin^{2}\theta + cos^{2}\theta = 1

  • sec^{2}\theta - tan^{2}\theta = 1

  • cosec^{2}\theta - cot^{2}\theta = 1

  • sin(A + B) = sinAcosB + cosAsinB

  • sin(A - B) = sinAcosB - cosAsinB

  • cos(A + B) = cosAcosB - sinAsinB

  • cos(A - B) = cosAcosB + sinAsinB


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