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Question
Discuss the continuity of the following function:
f(x) = sin x × cos x
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Solution
Let a be an arbitrary real number.
∴ f(a) = sin a × cos a
`lim_(x->a^+)` f(x) = `lim_(h->0)` [sin (a + h) cos (a + h)]
= `lim_(h->a^+)` [(sin a cos h + cos a sin h) (cos a cos h − sin a sin h)]
= sin a cos a
`lim_(x->a^-)` f(x) = `lim_(h->0)` [sin(a − h) cos (a − h)]
= `lim_(h->0)` [(sin a cos h − cos a sin h) (cos a cos h + sin a sin h)]
= sin a cos a
∴ `lim_(x->a^-)` f(x) = `lim_(x->a^+)` f(x) = f(a)
⇒ f(x) is continuous at x = a.
So, f(x) = sin x × cos x is everywhere continuous.
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