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Flashcards for McDougal Littell Geometry Chapter 7 Right Triangles

### Obtuse triangle

In a triangle with shorter sides a and b and longer side c, if a^2 + b^2 < c^2, then the triangle is obtuse

### Acute triangle

In a triangle with shorter sides a and b and longer side c, if a^2 + b^2 > c^2, then the triangle is acute

### Pythagorean Triple

Three positive integers that satisfy a^2 + b^2 = c^2, that is, they could be the three side lengths of a right triangle. Primitive triples include: 3, 4, 5; 5, 12, 13, and 8, 15, 17. More triples can be formed by multiplying each member of a primitive triple by the same multiplier; for example, since 3, 4, 5 is a triple, so is 6, 8, 10.

### 45-45-90 right triangle

Special right triangle: isosceles right triangle where the legs are congruent and the hypotenuse = leg * sqrt(2)

### 30-60-90 right triangle

Special right triangle: hypotenuse = shorter side ** 2; longer side = shorter side ** sqrt(3)

### sine

trigonometric ratio: abbreviation sin; the sine of an acute angle in a right triangle equals the side opposite the angle divided by the hypotenuse (sin A = opp/hyp)

### cosine

trigonometric ratio: abbreviation cos; the cosine of an acute angle in a right triangle equals the side adjacent to the angle divided by the hypotenuse (cos A = adj/hyp)

### tangent

trigonometric ratio: abbreviation tan; the tangent of an acute angle in a right triangle equals the side opposite the angle divided by the adjacent side (tan A = opp/adj)

### SOH CAH TOA

Mnemonic device to help remember the trig ratios in a right triangle: sin = opp/hyp; cos = adj/hyp; tan = opp/adj

### Inverse Trig Ratio

Gives us the measure of the angle whose sin/cos/tan is a given ratio value. "Undoes" sin, cos, or tan. Written using a "-1" (looks like an exponent, but isn't). Also called "arc," such as arcsin, arccos, arctan. Example: arcsin(1/2) = 30 degrees. Useful in finding missing angle values in right triangles.

### trigonometric ratios

Ratios formed by the sides of a right triangle. Useful in finding the missing sides of a right triangle given an angle and a side. Trigonometric ratios include sine (sin), cosine (cos), and tangent (tan). Other ratios (not covered in this chapter) are: cosecant, secant, and cotangent

### Solve a triangle

Means finding any missing angles and/or sides in a triangle. Methods to solve a right triangle include the Pythagorean theorem, triangle sum theorem (if given one acute angle in a right triangle, we can find the other by subtracting the acute angle's measure from 90), trig ratios, and inverse trig functions