Pythagoras' Theorem

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Pythagoras' Theorem practice questions

Secondary 2 topics, working towards the O-Level Mathematics 4052 syllabus. Every question below has a full worked solution.

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What this topic covers

Worked examples

Example 1

Isosceles △TUV has TU=TV=17TU = TV = 17 cm and UV=30UV = 30 cm. THTH is the perpendicular from TT to UVUV, where HH is the midpoint of UVUV. Find the length of THTH.
17 cm17 cm30 cm?TUVHNot drawn to scale
Show the worked solution
  • Since △TUV is isosceles and TH⊥UV,H is the midpoint of UV\text{Since }\triangle TUV\text{ is isosceles and } TH \perp UV, H \text{ is the midpoint of } UV
  • UH=UV2=302=15UH = \frac{UV}{2} = \frac{30}{2} = 15 cm
  • In △TUH, ∠THU=90°\text{In }\triangle TUH\text{, } \angle THU = 90°
  • TU2=TH2+UH2Pythagoras’ theoremTU^2 = TH^2 + UH^2 \quad \scriptsize\textit{Pythagoras' theorem}
  • 172=TH2+15217^2 = TH^2 + 15^2
  • TH2=172−152TH^2 = 17^2 - 15^2
  • TH2=289−225TH^2 = 289 - 225
  • TH2=64TH^2 = 64

Answer: 88

Example 2

Two vertical buildings are 1212 m and 2828 m tall and are 3030 m apart on level ground. A cable connects the tops of the two buildings. Find the length of the cable.
Show the worked solution
  • Vertical difference=28−12\text{Vertical difference} = 28 - 12
  • =16= 16 m
  • The cable forms the hypotenuse of a right-angled triangle with legs 16 m and 30 m.\text{The cable forms the hypotenuse of a right-angled triangle with legs 16 m and 30 m.}
  • Let the cable length=c\text{Let the cable length} = c m
  • c2=162+302Pythagoras’ theoremc^2 = 16^2 + 30^2 \quad \scriptsize\textit{Pythagoras' theorem}
  • c2=256+900c^2 = 256 + 900
  • c2=1156c^2 = 1156
  • c=34c = 34 m

Answer: 3434

Example 3

△MNP has MP=26MP = 26 cm, NP=24NP = 24 cm and MN=10MN = 10 cm. Show that △MNP is right-angled and find its area.
Show the worked solution
  • Arrange the sides in order: 10,24,26\text{Arrange the sides in order: } 10, 24, 26
  • The longest side is MP=26\text{The longest side is } MP = 26 cm
  • MP2=262MP^2 = 26^2
  • =676= 676
  • MN2+NP2=102+242MN^2 + NP^2 = 10^2 + 24^2
  • =100+576= 100 + 576
  • =676= 676
  • Since MP2=MN2+NP2, △MNP is right-angled.converse of Pythagoras’ theorem\text{Since } MP^2 = MN^2 + NP^2, \text{ }\triangle MNP\text{ is right-angled.} \quad \scriptsize\textit{converse of Pythagoras' theorem}

Answer: 120120

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O-Level Mathematics (4052), for Singapore secondary students. Math Amigo covers Secondary 1 to 4, both O-Level Mathematics and Additional Mathematics.

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