Since we want t to be in the interval [0,
] we have to
find all values of 2t in [0,
] and interval. That's because
since
then




Substitute
for




Multiply through by cos(2t) which we must require that
cos(2t) NOT EQUAL ZERO! because if it were zero we'd be
multiplying both sides of an equation by zero which is
not a valid operation.




with
Factor out sin(2t)


Use the zero-factor principle:
;
Taking the first equation
sin(2t) = 0
2t = 0,
,
,
,
so divide them all by 2 to solve for the values of t
t = 0,
,
,
,
.
So there are 5 solutions in the interval [0,
].
And there may be more from the second equation.
Taking the second equation:
But
is more than 1, in fact it's like 1.224744871
and no cosine can ever exceed 1 (except in much higher mathematics
courses, but forget that for now).
So there were no additional solutions from the
second equation.
So the only possible solutions are:
t = 0,
,
,
,
.
We must also check to see if any are extraneous solutions
because we multiplied through by
and had to
require that
,
But
is either 1 or -1 for each of those, never
0. So
t = 0,
,
,
,
.
are the only solutions in [0,
]
Edwin