$\cos^{-1}A+\cos^{-1}B=\pi/2 \Rightarrow \cos^{-1}A=\pi/2-\cos^{-1}B=\sin^{-1}B$, i.e., $A=\sin(\cos^{-1}B)=\sqrt{1-B^2}$.

$\dfrac{2}{3x}=\sqrt{1-\dfrac{9}{16x^2}}$

Square: $\dfrac{4}{9x^2}=1-\dfrac{9}{16x^2}$

Multiply by $144x^2$: $64=144x^2-81 \Rightarrow 144x^2=145 \Rightarrow x=\dfrac{\sqrt{145}}{12}$

Stress is defined as $\frac{\text{Force}}{\text{Area}}$ [cite: 457].

• Force (Weight) $W \propto \text{Volume} \times \text{density} \propto L^3$
• Area $A \propto L^2$
• $\text{Stress} \propto \frac{L^3}{L^2} \propto L$
• Since $L$ increases by $9$, the stress increases by a factor of $9$[cite: 457].

George Eastman introduced roll film and the simple Kodak box camera in 1888. This was revolutionary for several reasons:

• Before Eastman's roll film, photography required heavy glass plates, complex chemical baths, and specialist knowledge — making it impractical for rapid journalistic work
• The Kodak camera was simple enough for anyone to use (“You press the button, we do the rest” was Eastman's slogan), democratising photography
• Roll film was lighter and easier to load than glass plates, making field photography faster and more mobile
• This, combined with the halftone process (1881) and smaller cameras like the 35mm Leica (first marketed 1925), created the conditions for modern photojournalism

The photojournalist tradition — using shocking or revealing images to change public opinion and drive legislation — was enabled directly by these technological advances.