Ah okay so in differential equations you usually want the top variable isolated. To do this, multiply by dt and 2u and you get

Now just integrate both sides. The integral of 2u with respect to u is u². The integral of (2t + sec²(t) with respect to t is t² + ∫sec²(t)dt. The last part is just tan(x) because d/dt(tan(t)) is sec²(t) so just integrating gets us back. Now we have

Where c and k are arbitrary constants. Subtracting c from k and you get

Where b is another constant. To find b, just plug in u(0) = -1 where u is -1 and t is 0. This becomes

tan(0) is 0 so b = 1. Take the plus or minus square root on both sides and you finally get

But Brainly didn't let me do but juat remember there is a plus or minus square root on the left.
Answer:
458
Step-by-step explanation:
Answer:
Step-by-step explanation:
it is given that Square contains a chord of of the circle equal to the radius thus from diagram

If Chord is equal to radius then triangle PQR is an equilateral Triangle
Thus 
In triangle PQO applying Pythagoras theorem




Thus length of Side of square 
Area of square
Area of Circle
Ratio of square to the circle
Answer:
19) (
)^2 = 
20) -
= -81
21)
= 16
Step-by-step explanation:
The only wrong ones are
19) (
)^2 = 
20) -
= -81 ... negative is not inside a parenthesis that's why it is still negative
21) you can add another way is
= 16
Everything else looks good. Great job!