Hello everyone! I’m also a math learner. For me, trigonometric formulas are the most basic array in the curriculum. However, some students still feel it difficult to memorize all these formulas? Don’t worry! Today, I would like to introduce to you one simple method to remember these formulas for a long time with APP RESUMIND. Let’s scroll down to the blue text for detailed instructions!

## 1. Tips to learn Trigonometric Formulas super-fast: Basic trigonometric formulas

• sin2x + cos2x = 1
• tan x = sin x / cos x
• cot x = cos x / sin x
• tan x * cot x = 1
• 1 / cos2x = 1 + tan2x
• 1 / sin2x = 1 + cot2x

## 2. Tips to learn Trigonometric Formulas super-fast: The addition formula

• sin(a + b) = sin a * cos b + cos a * sin b
• cos(a + b) = cos a * cos b – sin a * sin b
• In short, sin = sin cos + cos sin, cos = cos cos – sin sin
• tan(a + b) = (tan a + tan b) / (1 – tan a * tan b)

## 3. Tips to learn Trigonometric Formulas super-fast: The multiplication formula and the downgrade formula.

• sin 2x = 2 * sin x * cos x
• cos 2x = cos2x – sin2x
• sin x * cos x = sin 2x / 2
• sin2x = (1 – cos 2x) / 2
• cos2x = (1 + cos 2 x) / 2
• sin 3x = 3 * sin x – 4 * sin3x
• cos 3x = 4 * cos3x – 3 * cos x

## 4. The formula converts the product to the sum.

• cos a * cos b = [ cos(a + b) + cos(a – b) ] / 2
• sin a * sin b = -[ cos(a + b) – cos(a – b) ] / 2
• sin a * cos b = [ sin(a + b) + sin(a – b) ] / 2

## 5. The formula converts the sum to the product.

• cos a + cos b = 2 * cos [(a + b) / 2] * cos [(a – b) / 2]
• cos a – cos b = – 2 * sin [(a + b) / 2] * sin [(a – b) / 2]
• sin a + sin b = 2 * sin [(a + b) / 2] * cos [(a – b) / 2]
• sin a – sin b = 2 * cos [(a + b) / 2] * sin [(a – b) / 2]
• Way to remember quickly:
• cos + cos = 2 cos cos
• cos – cos = – 2 sin sin
• sin + sin = 2 sin cos
• sin – sin = 2 cos sin