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Zorluk: KolayTrigonometric Ratios and Identities

If cos(θ)=725\cos(\theta) = \frac{7}{25} and 0<θ<π20 < \theta < \frac{\pi}{2}, what is the value of sin(π2θ)\sin\left(\frac{\pi}{2} - \theta\right)?

  1. A
    2425\frac{24}{25}
  2. 725\frac{7}{25}Cevap
  3. C
    257\frac{25}{7}
  4. D
    1825\frac{18}{25}

Cevap

725\frac{7}{25}
The correct answer is 725\frac{7}{25} because the co-function identity states that for any angle θ\theta, the sine of its complement, π2θ\frac{\pi}{2} - \theta, is equal to the cosine of θ\theta. Given that cos(θ)=725\cos(\theta) = \frac{7}{25}, it follows that sin(π2θ)=725\sin\left(\frac{\pi}{2} - \theta\right) = \frac{7}{25}.

Adım Adım Çözüm

1
Identify the relevant trigonometric identity.
Use the co-function identity sin(π2x)=cos(x)\sin\left(\frac{\pi}{2} - x\right) = \cos(x).
Since the angle is given in radians, the complementary angle identity relates the sine of the complement to the cosine of the original angle.
2
Substitute the given value.
Since cos(θ)=725\cos(\theta) = \frac{7}{25}, then sin(π2θ)=725\sin\left(\frac{\pi}{2} - \theta\right) = \frac{7}{25}.
Direct substitution of the given cosine value into the identity yields the final answer.

Anahtar Kavram

Co-function identities relate the sine and cosine of complementary angles.
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