In $\Delta ABC$, $AB=16$ cm, $BC=12$ cm and $AC=20$ cm. $BA$ is produced to $D$ and \(AD

Question

In $\Delta ABC$, $AB=16$ cm, $BC=12$ cm and $AC=20$ cm. $BA$ is produced to $D$ and $AD=8$ cm. Explain why $\angle ABC$ is a right angle. Find the area of $\Delta DAC$. Write down the value of $\cos \angle DAC$.

Accepted Answer

(i) $\angle ABC=90^\circ$ by the converse of Pythagoras' theorem (ii) $48\text{ cm}^2$ (iii) $-\frac{4}{5}$

The Geometry of Trigonometric Ratios: From Coordinate Points to Sine and Cosine

The Geometry of Trigonometric Ratios: From Coordinate Points to Sine and Cosine

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