Question

Sam used his calculator to find cos 1.75 He wrote down cos 1.75 = .999 How could Sam recognize that his answer is incorrect?

Answer 1

Answer on Question #57976 – Math – Trigonometry

Question

Sam used his calculator to find cos 1.75. He wrote down cos $1.75 = .999$ How could Sam recognize that his answer is incorrect?

Solution

Since pi is 3.14, 1.75 should be about half of pi so $\cos(1.75)$ should be in the ballpark of $\sqrt{2}$ or .7 ish. Clearly his calculator is in degree mode since $\cos(1.75$ degrees) is about .999.

Even more obvious, $\mathrm{pi} / 2 < 1.75 < \mathrm{pi}$.

So on the unit circle it will be in the second quadrant.

So $\cos(1.75)$ is negative.

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