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Date & Time

Timezone Conversion Without Losing Your Mind

IANA timezone database is the source of truth. Three-letter abbreviations like EST and IST are ambiguous and unsafe.

Nov 30, 2025

Math

Quadratic Formula: When Factoring Fails

For ax^2 + bx + c = 0, x = (-b +/- sqrt(b^2 - 4ac)) / 2a. The discriminant tells you what kind of roots to expect.

Nov 26, 2025

Taxes

Tax Deductions for Freelancers: Maximize Your Write-Offs

Most freelancers miss deductions. Here's a comprehensive list of what you can write off: office supplies, software, equipment, and more.

Nov 25, 2025

Date & Time

Working Days Calculator: What Counts as a Business Day

Business days exclude weekends and "federal holidays" — but federal holidays vary by country and by industry.

Nov 25, 2025

Health

TDEE and BMR: How Many Calories Do You Actually Burn?

BMR is what you burn at rest. TDEE adds your activity. Knowing both is the foundation of any sustainable diet.

Nov 23, 2025