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There is also an exercise in sine theorem and cosine theorem Sina + sinc = SINB how to get 2sina + C / 2 * cosa-c / 2 = 2sinb from sum difference product formula
From the sum difference product formula sin α + sin β = 2Sin [(α + β) / 2] · cos [(α - β) / 2]
We obtain sin a + sin C = 2Sin [(a + C) / 2] · cos [(A-C) / 2]
So 2Sin [(a + C) / 2] · cos [(A-C) / 2] = SINB
But not 2Sin (a + C) / 2 * cos (A-C) / 2 = 2Sin B
Why is the total resistance of a parallel circuit smaller than that of any of the sub resistors
Why?
Parallel is quite wide with the road, and the sub resistor road is narrow, so the current is relatively large
So it's equivalent to a small resistance
In addition, it can be proved by the formula
Why is the total resistance of the parallel circuit smaller than that of any sub resistance?
This is a question in the book, a short answer
There are n resistors in parallel. The resistors are divided into R1, R3, R3 RN total resistance is r, 1 / r = 1 / R1 + 1 / r2 + 1 / R3 +1 / RN if R1 (or any other resistor) is the smallest of the N resistors, then 1 / r = 1 / R1 + 1 / r2 + 1 / R3 +1 / RN > 1 / R1, 1 / R > 1
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