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2023-II-35

Posted on 28-07-2023 By app.cch No Comments on 2023-II-35
Ans: D

Rewrite the function of the graph to vertex form, we have

$\begin{array}{rcl}
f(x) & = & 3x^2+18mx+22m^2 \\
f(x) & = & 3(x^2+6mx)+22m^2 \\
f(x) & = & 3\left[x^2+6mx +\left(\dfrac{6m}{2}
\right)^2-\left(\dfrac{6m}{2}\right)^2\right]+22m^2 \\
f(x) & = & 3[(x+3m)^2-9m^2]+22m^2\\
f(x) & = & 3(x+3m)^2-5m^2
\end{array}$

Hence, we have

$\begin{array}{rcl}
y & = & -f(3x) \\
y & = & -[3(3x+3m)^2-5m^2] \\
y & = & -27(x+m)^2+5m^2 \ \ldots\unicode{x2460}
\end{array}$

I may not be true. From $\unicode{x2460}$, the $x$-coordinate of the vertex of the graph is $-m$. The statement is true only when $m=0$.

II must be true. From $\unicode{x2460}$, the $y$-coordinate of the vertex of the graph is $5m^2$.

III must be true. From $\unicode{x2460}$, the equation of the axis of symmetry of the graph is $x=-m$, i.e. $x+m=0$.

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2023, HKDSE-MATH, Paper 2 Tags:Transformations

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3D Problems (41) Basic Functions (13) Basic Geometry (68) Binomial Theorem (7) Change of Subject (32) Complex Numbers (16) Coordinates (46) Differentiation (16) Equations of Circle (54) Equations of Straight Line (43) Estimations and Errors (35) Factorization (39) Graph of Functions (3) Inequality (39) Integration (15) Laws of Indices (43) Linear Programming (21) Locus (13) Logarithm (34) Mathematical Induction (7) Matrices (4) Mensuration (98) Numeral System (19) Percentage (42) Polynomials (49) Probability (85) Properties of Circles (56) Quadratic Equations and Functions (57) Rate and Ratio (30) Rational Functions (20) Sequences (66) Simultaneous Linear Equations (27) Statistics (122) System of Linear Equations (3) Transformations (44) Trigonometry (M2) (7) Trigonometry and Its Applications (67) Variations (38) Vectors (3)

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