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# Another problem simplifying symbolic trigonometric expressions

I am testing Sage with the notebook interface, and I want to simplify this trigonometric symbolic expression:

var('x1','x2')
exp1=sin(x1)*cos(x2)+sin(x2)*cos(x1)
print(exp1.trig_simplify())

Sage does not simplify this expression and the result is:

cos(x2)*sin(x1) + cos(x1)*sin(x2)

As you can see the result show be:

sin(x1+x2)

Is there any to simplify trigonometric functions applied to the addition or the subtraction of two values? Thanks

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## 1 answer

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You must use trig_reduce():

sage: exp1.trig_reduce()
sin(x1 + x2)

The reverse operation is trig_expand():

sage: exp2 = sin(x1 + x2)
sage: exp2.trig_expand()
cos(x2)*sin(x1) + cos(x1)*sin(x2)
more

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Asked: 2018-01-11 03:40:29 -0600

Seen: 387 times

Last updated: Jan 11 '18