Question

In Exercises 27-32, sketch the quadric surface. \(z-y^{2}+x^{2}=0\)

Short answer

The equation represents a hyperbolic paraboloid.

Step-by-step solution

Recognize the Equation Type

The given equation is \(z - y^2 + x^2 = 0\). In the context of quadric surfaces, we identify terms that are squared. This has terms involving \(x^2\), \(y^2\), and a linear term in \(z\). Such terms often represent parabolic or hyperbolic surfaces.

Rearrange the Equation

Rearrange the equation to isolate \(z\): \[ z = y^2 - x^2 \] This rearrangement helps us better understand the form of the surface and visualize it more easily.

Identify the Surface Type

The equation \(z = y^2 - x^2\) is the equation of a hyperbolic paraboloid. This is a saddle-shaped surface, which can be identified because the \(y^2\) and \(x^2\) have opposite signs.

Sketch the Surface

To sketch a hyperbolic paraboloid, consider the traces: - In the \(x-z\) plane: set \(y=0\), so \(z = -x^2\) which is a downward-opening parabola. - In the \(y-z\) plane: set \(x=0\), so \(z = y^2\) which is an upward-opening parabola. - In the \(x-y\) plane: set \(z=0\), the equation becomes \(y^2 = x^2\), which are lines \(y = x\) and \(y = -x\). These traces will help in sketching the curve as a saddle shape.

Describe the Geometry

The hyperbolic paraboloid is a doubly ruled surface which means it can be formed by straight lines. Its center is at the origin, and it extends infinitely in all directions with a saddle-like curvature.

Key concepts

Hyperbolic Paraboloid

A hyperbolic paraboloid is a fascinating type of quadric surface that has a distinctive saddle shape. It is defined by the equation \( z = y^2 - x^2 \), where the presence of both positive and negative squared terms indicates its peculiar geometry. The term 'paraboloid' suggests a relation to parabolas. Here, it means the surface contains parabolic curves, yet arranged in such a way to form a saddle.

This shape is known for its unique structural properties, often making it a prime choice in architectural designs, like rooftops, due to its strength and aesthetic appeal. In essence, the hyperbolic paraboloid presents a harmonious blend of complexity and symmetry.

Saddle Surface

The saddle surface is another term representing the hyperbolic paraboloid. When imagined, think of the shape of a saddle, which curves upwards in one direction and downwards in the other. This curvature is what gives it the nickname 'saddle surface'.

Unlike flat or cylindrical surfaces, the saddle surface features a central point of minimal curvature, making it a point of balance. This center is at the origin in the coordinate plane. The surface 'saddles' its way infinitely, without reaching any boundaries, adding to its intriguing geometric properties.

Parabolic Traces

Analyzing a hyperbolic paraboloid, parabolic traces serve as a gateway to understanding its complex geometry. By examining cross-sectional cuts, we can identify various parabolic shapes depending on the plane chosen.

For example, when slicing through the \(x-z\) plane (setting \(y=0\)), the resulting graph is a downward-opening parabola: \( z = -x^2 \). Conversely, in the \(y-z\) plane (setting \(x=0\)), the trace is an upward-opening parabola: \( z = y^2 \). These perpendicular parabolas align to construct the complete saddle shape, with the intersection at the origin producing lines like \(y = x\) and \(y = -x\) when \(z=0\).

The smooth transition between the upward and downward openings reveals the smooth, continuous nature of the surface.

Ruled Surfaces

The hyperbolic paraboloid is a remarkable example of what mathematicians call a ruled surface. This means it can be constructed entirely from straight lines, despite its curved appearance.

Visualize it as a surface woven from threads stretched straight, defining lines that intersect over the curve. It has not just one, but two families of such lines, lending it a doubly-ruled attribute.

Ruled surfaces hold a special place in both geometry and practical applications. Their unique framework, derived from simple linear forms, showcases the astonishing versatility of geometric structures. In architecture, this concept grants rise to efficient yet visually stunning designs.