Step-by-step explanation:
With what?...........
.....
Answer:
See below.
Step-by-step explanation:
We know that
tanA + tan B
tan (A + B) = ---------------------
1 - tanAtanB
Substituting for A + B
tan (A + B) = tan pi/4 = 1.
tanA + tan B
So ------------------ = 1
1 - tanAtanB
Therefore tanA + tan B = 1 - tanAtanB.
The best way to multiply complicated problems mentally* is to break them into chunks.
Start with 20 times 8 to get 160, and then 8 times 5 to get 40. Add these together to get 200. 200 times 3 is 600, and 20 times 200 is 4000. Add these together to get your final answer, 4600.
In other words 8 x 20 + 8 x 5 = 200 200 x 3 + 200 x 20 = 4600
*I assumed you meant mentally, because otherwise you'd just multiply longhand, multiplying two of the three numbers and then multiplying their product with the third.