Handwritten Calculus on a Whiteboard

[Format] Landscape 16:9 gig cover, plainly photographed whiteboard surface. Matte white panel, dry-erase marker strokes, slight warm colour cast and lens vignetting; candid and unretouched. No text overlay, no design furniture. No watermark, no personal names. [Layout] The entire frame is a single whiteboard surface — no panels, no borders, no coloured blocks. Handwriting occupies the left two-thirds at a slight upward slant, and the right third carries one large hand-sketched diagram. Top-left: a single short equation line. Below it: a two-line worked formula block, the first line much larger and more emphatic with an indented continuation below. Right side, vertically centred: a tall hand-drawn solid-of-revolution sketch — a vertical axis, a horizontal axis with arrowheads at both ends, a tall hatched cylinder form drawn in blue, a yellow vertical rectangle nested inside it, and a red closed loop curve swept over the middle, with short tick marks and minus-one and plus-one labels near the ends. The bottom edge cuts off the final formula line mid-stroke, so the writing runs out of the frame. [Subject] None — no person, no product and no overlaid graphics. Only handwriting and pen sketches on white. [Headline] There is no typography; the text layer is entirely handwritten marker. Top-left, a short slanted equation reading like 'y = 2 cos x' in black. Mid-left, a large volume-of-revolution integral beginning 'V = 2' with a definite-integral sign, lower and upper limits, a squared bracketed term and a differential at the end, followed by two smaller expansion lines stacked beneath it. Right side, small black axis labels reading minus one and one. Red, blue, yellow and green are used only inside the diagram, never for text. [Badges] None. [Mood] Whiteboard white with black ink and red, blue, yellow and green pen accents. Raw, unglamorous and highly instructive — unmistakably a photograph of real teaching work rather than a designed advertisement, which is exactly the point.