Math Problem Statement

XYZ est un triangle rectangle en y tel que XY = 5 cm et XZ = 13 cm. Trouve la valeur de: tg X + tg Z, cos X cos Z − sin X sin Z, sin X cos Z + cos X sin Z.

Solution

The problem involves a right-angled triangle XYZXYZ, with XY=5cmXY = 5 \, \text{cm} and XZ=13cmXZ = 13 \, \text{cm}. The goal is to find the values for the expressions given:

  1. A: tanX+tanZ\text{A: } \tan X + \tan Z
  2. B: cosXcosZsinXsinZ\text{B: } \cos X \cos Z - \sin X \sin Z
  3. C: sinXcosZ+cosXsinZ\text{C: } \sin X \cos Z + \cos X \sin Z

Step 1: Identify triangle sides

Since this is a right-angled triangle, we can use the Pythagorean theorem to find the length of the third side YZYZ:

YZ=XZ2XY2=13252=16925=144=12cm.YZ = \sqrt{XZ^2 - XY^2} = \sqrt{13^2 - 5^2} = \sqrt{169 - 25} = \sqrt{144} = 12 \, \text{cm}.

Step 2: Calculate the trigonometric values

  • For X\angle X: sinX=XYXZ=513,cosX=YZXZ=1213.\sin X = \frac{XY}{XZ} = \frac{5}{13}, \quad \cos X = \frac{YZ}{XZ} = \frac{12}{13}.

  • For Z\angle Z (since ZZ is complementary to XX, sinZ=cosX\sin Z = \cos X and cosZ=sinX\cos Z = \sin X): sinZ=1213,cosZ=513.\sin Z = \frac{12}{13}, \quad \cos Z = \frac{5}{13}.

Step 3: Evaluate the given expressions

  1. A: tanX+tanZ\tan X + \tan Z tanX=sinXcosX=512,tanZ=sinZcosZ=125.\tan X = \frac{\sin X}{\cos X} = \frac{5}{12}, \quad \tan Z = \frac{\sin Z}{\cos Z} = \frac{12}{5}. So, tanX+tanZ=512+125=25+14460=16960.\tan X + \tan Z = \frac{5}{12} + \frac{12}{5} = \frac{25 + 144}{60} = \frac{169}{60}.

  2. B: cosXcosZsinXsinZ\cos X \cos Z - \sin X \sin Z (this is the formula for cos(X+Z)\cos(X + Z), and since X+Z=90X + Z = 90^\circ, cos90=0\cos 90^\circ = 0): [ \cos X \cos Z - \sin X \sin Z = 0.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Right-Angle Triangle
Pythagorean Theorem

Formulas

Pythagorean Theorem: a² + b² = c²
Sine Rule: sin θ = opposite / hypotenuse
Cosine Rule: cos θ = adjacent / hypotenuse
Tangent: tan θ = opposite / adjacent
Sum of Angles: cos(X + Z) = 0 since X + Z = 90°

Theorems

Pythagorean Theorem

Suitable Grade Level

Grades 9-11