Part of ALG-02 — Complex Numbers

JEE Problem-Solving Strategies

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Strategy 1: Substitute z = x + iy early For equations involving both z and z-bar, immediately write z = x+iy and z-bar = x-iy. Separate real and imaginary parts.

Strategy 2: Use |z|^2 = z * z-bar When you see |z|^2, replace with zz-bar. When you see zz-bar, recognize it as |z|^2. This interconversion is used in almost every problem.

Strategy 3: Polar form for powers/products Any problem involving znz^n, z1*z2, or z1/z2 is faster in polar form. Convert, operate, convert back.

Strategy 4: Geometry for locus If the equation involves |z - z1|, arg(z - z1), or similar, think geometrically before algebraically.

Strategy 5: Cube roots of unity simplification Whenever w appears, immediately use 1 + w + w2w^2 = 0 and w3w^3 = 1 to reduce expressions. Replace w2w^2 with -1-w or w with -1-w2w^2 as needed.

Strategy 6: Section formula Point dividing z1z2 in ratio m:n internally: z = mz2+nz1(m+n)\frac{mz2 + nz1}{(m+n)}. Externally: z = mz2nz1(mn)\frac{mz2 - nz1}{(m-n)}.

Time allocation: Most JEE complex number problems should be solvable in 2-3 minutes with the right approach.

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