Practise free online CBT mock test for West Bengal Board (WBBSE) Class 10 (Madhyamik) Mathematics Chapter 11 'Construction of Circumcircle and Incircle of a Triangle'. 20 MCQs, 20-minute timer, instant scorecard, and step-by-step solutions aligned with official board syllabus.
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In the WBBSE Class 10 Madhyamik Mathematics curriculum (Ganit Prakash / গণিত প্রকাশ), Theorems related to Circle (Chapter 3) forms the foundation of secondary Euclidean geometry (বৃত্ত সম্পর্কিত উপপাদ্য). A circle is defined as the geometric locus of all points in a plane equidistant from a fixed point called the centre ($O$), with the constant distance denoted as the radius ($r$). A straight line segment connecting any two points on the circumference is known as a chord ($AB$). The longest chord passing through the centre is the diameter ($d = 2r$).
The fundamental geometric pillars of this chapter are established by Theorems 32 and 33: "The perpendicular drawn from the centre of a circle to a chord which is not a diameter, bisects the chord." Conversely, "The line segment joining the centre of a circle and the midpoint of a chord (not a diameter) is perpendicular to the chord." If $OM \perp AB$, then $AM = MB = \frac{1}{2}AB$, and inside right-angled triangle $\triangle OMA$, the Pythagorean relation governs all metric dimensions: $$r^2 = d^2 + \left(\frac{L}{2}\right)^2$$ where $r = OA$ is the radius, $d = OM$ is the perpendicular distance from the centre to the chord, and $L = AB$ is the chord length.
Furthermore, chords of a circle equidistant from the centre are equal in length ($d_1 = d_2 \iff L_1 = L_2$), and conversely, equal chords are strictly equidistant from the centre. In concentric circles (circles sharing the same centre with radii $r < R$), a chord of the outer circle tangent to the inner circle is bisected at the point of tangency by the radius of the inner circle. Thorough conceptual and algebraic mastery of these theorems guarantees 100% marks in both geometric riders (proofs) and objective numerical problems in the WBBSE Madhyamik board examination.
Mastering centre-chord perpendicularity $OM \perp AB$, chord bisection $AM = \frac{L}{2}$, and the Pythagorean metric $r^2 = d^2 + (L/2)^2$ guarantees complete success in WBBSE Madhyamik circle geometry.
| Term / Formula | Type | Definition / Meaning | Explanation / Notes | Example / Usage |
|---|---|---|---|---|
| Theorem 32 | Theorem | Line joining centre to chord midpoint is perpendicular: OM ⊥ AB. | Line segment joining circle centre to chord midpoint is perpendicular to the chord. | "If M is midpoint of chord AB, then ∠OMA = 90°." |
| Theorem 33 | Theorem | Perpendicular from centre bisects chord: AM = MB = L/2. | Perpendicular drawn from centre of circle to a chord bisects the chord. | "If OM ⊥ AB, then AM = MB = AB/2." |
| Chord-Radius Pythagorean Metric | Master Formula | r² = d² + (L/2)² | Radius squared equals perpendicular distance squared plus half-chord squared. | "If r = 10 cm, d = 6 cm, then half-chord = √(100 - 36) = 8 cm, chord = 16 cm." |
| Perpendicular Distance (d) | Derived Formula | d = √(r² - (L/2)²) | Perpendicular distance from centre = √(radius² - (chord/2)²). | "For r = 13 cm and chord = 24 cm, d = √(169 - 144) = 5 cm." |
| Chord Length (L) | Derived Formula | L = 2 · √(r² - d²) | Total chord length = 2 × √(radius² - distance²). | "For r = 5 cm and d = 3 cm, L = 2 × √(25 - 9) = 8 cm." |
| Equidistant Chords Property | Property | L₁ = L₂ ⇔ d₁ = d₂ | Equal chords are equidistant from the centre and vice versa. | "Two chords of 14 cm each are at identical distances from centre." |
| Parallel Chords on Opposite Sides | Distance Rule | Total distance D = d₁ + d₂ | Distance between parallel chords on opposite sides of centre is the sum of distances. | "If d₁ = 4 cm and d₂ = 3 cm, then distance between them is 4 + 3 = 7 cm." |
| Concentric Circles Tangent Chord | Identity | L = 2√(R² - r²) | Length of outer chord touching inner circle of radius r. | "For R = 5 cm, r = 3 cm, chord length L = 2√(25 - 9) = 8 cm." |
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