if tanθ = \(frac{3}{4}\), 180° < θ < 270°, find the value of cosθ.

  • A \(\frac{4}{5}\)
  • B \(\frac{3}{5}\)
  • C -\(\frac{4}{5}\)
  • D -\(\frac{3}{5}\)
waec 2021mathematics

The correct answer is C. -\(\frac{4}{5}\)

tanθ = \(frac{3}{4}\) â†’ tanθ = 0.75

θ = tan\(^{-1}\)[0.75] â†’ 36.8698°

cosθ = cos[36.8698°] 

→ 0.800 or  \(frac{4}{5}\) 

However; in the third quadrant Cosine is negative

i.e -\(frac{4}{5}\)

Previous question Next question