example lessons, explained step by step
Every lesson below was made by the Doubtster video engine: a voice explains each step and why, while the working is written on the board. Each page has the full video and transcript.
maths · 2:01Integral of x sin x from 0 to π/2, solved by parts
Watch the integral of x sin x from 0 to π/2 worked out step by step with integration by parts: choosing u and dv, plugging in, the limits, and a check. The answer is 1.
physics · 1:50Block sliding down a 30° incline with friction: find the acceleration
A block slides down a 30° incline with μ = 0.2. See the force diagram, Newton's second law along the slope, why N = mg cos θ, and the answer a ≈ 3.20 m/s², explained step by step.
coding · 3:25Median of two sorted arrays, explained with binary search
The median of two sorted arrays problem (LeetCode 4) explained step by step: the partition idea, moving the cut with binary search, a worked example and the Python code, in O(log min(m, n)) time.
biology · 2:22Why is DNA replication semiconservative?
Why DNA replication is called semiconservative: each new DNA molecule keeps one parental strand and gets one new strand. Each option explained, a two-round strand diagram, and the Meselson and Stahl experiment.